Summary of the IPCC’s 5th annual report at the Cambridge Centre for Climate Science

ipcc_small

This week I wrote a blog post for the Cambridge Centre for Climate Science (CCfCS). It’s a summary of an afternoon of talks about the IPCC 5th annual report on climate change. The event was organised by both the CCfCS and the Cambridge Institute for Sustainable Leadership (CISL). UPDATE: the link to the website has broken so I have copied and pasted my report below.

A more detailed summary of both Working Group 1 (The Scientific Basis) and Working Group 2 (Impacts and Adaptation) can be found in previous posts I’ve written.

CCfCS – IPCC AR5 Synthesis Report Discussion Meeting

This week the Cambridge Centre for Climate Science (CCfCS) and the Cambridge Institute for Sustainable Leadership (CISL) hosted an afternoon of presentations and discussions about the 5th Intergovernmental Panel on Climate Change (IPCC) report (AR5).  The meeting coincided with the release of the ‘Synthesis’ report which was the final document to be released for AR5.

The meeting was organised by Dr Michelle Cain (CCfCS) and chaired by Dr Eliot Whittington (CISL). Four speakers spoke about the three working group reports and the IPCC’s impact on policy. A panel discussion followed where audience members could ask questions and give comments. Lastly, the afternoon concluded with an opportunity for networking over a wine reception.

The first of the four speakers was Prof. Eric Wolff from the Department of Earth Sciences, formally from the British Antarctic Survey. Professor Wolff gave a clear summary of the working group (WG) 1 report which assesses ‘The Physical Science Basis’, as well as a brief overview of the history of the IPCC. The IPCC is a UN indorsed organisation set up by the United Nations Environment Program (UNEP) and the World Meteorological Organisation (WMO) in 1988. The published reports released every ~5 years aim to assess “the scientific, technical and socio-economic information relevant to understanding the scientific basis of risk of human-induced climate change“.

WG1 discusses both past and present observations are conducted, and how the use of complex computer models help to understand the climatological processes occurring in the world. Observations including sea ice extent, atmospheric and ocean temperature, ocean acidity and sea level show concurrently the world is warming. The rate of change is at least 10 times faster than the warming from the last ice age. Computer analysis shows that these observed changes cannot be replicated without the consideration of anthropogenic interactions to the environment (i.e CO2 has risen 40% in the last two centuries). Future ‘pathways’ the world can adopt show at least a 2 degree warming by the year 2100, if an aggressive strategy is adopted to reduce GHG emissions. A ‘business as usual’ pathway shows an increase of 4-5 degrees. This would have major impacts on the world as the last ice age was only 5 degrees cooler than today.

The second speaker was Prof. Douglas Crawford-Brown from the Cambridge Centre for Climate Change Mitigation Research who summarised the WG2 report: Impacts, Adaptation and Vulnerability. Five themes (listed below) regarding impacts were addressed in this report. The report was criticised however for not addressing each theme with equal weighting.

  • Unique and threatened systems
  • Extreme weather events
  • Distribution of impacts
  • Global aggregate impacts
  • Large scale singular effects

Both global and regional impacts were addressed and the idea of ‘risk’ was commonly used as an analytical framework throughout the report, whereas in 2009 the AR4 WG2 report concentrated more on pure relevance scenarios. Future impacts were discussed using the same pathways described in the WG1 report. A region’s vulnerability and ability to adapt was also assessed.

The WG3 report: Mitigation of Climate Change, was summarised by the third speaker Dr David Reiner from the Energy Policy Research Group in the Judges Business School. Dr Reiner started his talk by advising that for this WG the technical summary (TS) which, although longer, provides a more detailed analysis of the scientific data than the summary for policy makers. The report starts by explaining that GHG emissions are continuing to rise on the global scale despite many reduction policies in place. This is due to increasing emission rates from more developing nations. Dr Reiner explained that the primary purpose of WG3 was to assess multiple mitigation pathways and its impact on the economy. Global baseline projections for the Kaya factors (population, GDP per capita, energy use per unit of GDP, carbon emissions per unit of energy consumed) were also shown in the report. An attempt to quantify the economic cost of mitigation strategies and other co-benefits to reducing GHG emissions (e.g better air quality) were also highlighted. Of the three working group reports, the third was the least well reviewed after publication, with the economic models being questioned.

This was also mentioned in the final speaker’s talk ‘A policy perspective on the IPCC’ by Prof David MacKay who was the former chief scientific advisor to the Department for Energy and Climate Change (DECC), and now works in the Engineering Department of Cambridge University. Professor MacKay provided constructive criticism for some areas of improvement for future reports. The quantification of risk and the clarification of uncertainty were stressed to be particularly useful for determining future policies.

A panel discussion, lasting ~90 minutes, allowed the audience to ask questions and offer comments. Topics including carbon sequestration, the format of future IPCC reports, the role of both public and private sectors in CC mitigation, and the portrayal of scientific facts and figures were all addressed. Less formal discussions then continued at the wine reception.

More information about the three working group reports can be found in their respective technical summaries (TS) or their summary for policy makers (SPM):

WG1  WG2  WG3

Advertisements

Key Findings from the IPCC Working Group 2: Impacts & Risks from Climate Change

Introduction

The IPCC (Intergovernmental Panel on Climate Change) consists of three working groups who publish reports every 6 years describing the current understanding of all aspects of climate change (CC). The previous blog post (Key Figures from the IPCC’s AR5 Report) gives an introduction into the IPCC and explains the key figures published by the First Working Group last winter which concentrates on the scientific evidence of CC. This blog post summarises the highlights from the Second Working Group (WG2) which aimed to assess the risks associated with CC, particularly Impacts, Adaptation and Vulnerability.

WG2’s Summary for Policy Makers, which this post is based upon, assesses relevant scientific, technical and socioeconomic literature. Such literature is comprised of empirical observations, experimental results, process-based understanding, statistical approaches, simulation and descriptive models as well as expert judgement.

NB: For descriptions of the confidence and certainty values mentioned in this post please see this previous post on the WG1 report.

Current Observed Impacts, Vulnerability, and Exposure

The figure below summarises the observed impacts around the world in the last few decades. A hollow symbol means that the evidence suggests CC has had a minor impact, and a filled symbol represents a major CC contribution. The rectangular bars beside each symbol represent the confidence associated with each impact. A summary of the major themes found throughout the impacts stated on this map are listed below. All statements are stated to have high or medium confidence levels.

  • Changes in precipitation or melting snow / ice is altering some regions’ hydrological systems, which can affect water resources and quality.
  • Many species have shifted their geographic ranges, seasonal migration times, abundances etc. A few species have become extinct due to current CC.
  • Negative impacts of CC on crop yields currently outweigh positive impacts. Positive impacts are mainly localised to the Northern hemisphere higher latitude regions.
  • Currently, the impact of CC on worldwide human health is minimal when compared with other contributing factors. It should be noted that there has been an increase in heat related mortality and a decrease in cold related mortality.
  • Climate extremes, for example, heat waves, droughts, floods (which are expected to increase in the future) are a significant vulnerability for some ecosystems.
  • Climate related hazards aggravate other stressors that impact human life, especially for people living in poverty. For example, food price increases due to lower crop yields. Observed positive impacts are limited and often indirect, for example, diversification of agricultural practices.
Widespread impacts in a changing world. (A) Global patterns of impacts in recent decades attributed to climate change, based on studies since the AR4. Impacts are shown at a  range of geographic scales. Symbols indicate categories of attributed impacts, the relative  contribution of climate change (major or minor) to the observed impact, and confidence in  attribution.

Widespread impacts in a changing world. (A) Global patterns of impacts in recent decades attributed to climate change, based on studies since the AR4. Impacts are shown at a range of geographic scales. Symbols indicate categories of attributed impacts, the relative contribution of climate change (major or minor) to the observed impact, and confidence in attribution.

The following diagram shows regional examples of the impacts described in the previous paragraph. For a more comprehensive list of impacts please see the Summary for Policy Makers Table 1. All statements listed below have confidence levels shown in brackets after each impact.

 Constructed using data from the WG2 SPM Table 1.

The figure below shows the average percentage change in crop yield. The two blue bars to the left show all crops grouped as growing in tropical or temperate climates. The four orange bars on the right are the most common crops worldwide. It has been observed on the whole that CC has had a negative impact on yields of most crops worldwide.

(C) Summary of  estimated impacts of observed climate changes  on yields over 1960-2013 for four major crops in temperate and tropical regions, with the  number of data points analyzed given within parentheses for each category.

(C) Summary of estimated impacts of observed climate changes on yields over 1960-2013 for four major crops in temperate and tropical regions, with the number of data points analyzed given within parentheses for each category.

Risks in the Future

The second half of the summary for policy makers concentrates on the future risks and possible benefits CC will bring to the world. The magnitude and rate of CC is also taken into consideration. The IPCC Working Group 1 used four representative concentration pathway (RCP) scenarios to predict the average global temperature leading up to 2100. For definitions of the RCP scenarios please read my last post. The following risks predicted by the WG2 all occur in at least one of the RCP scenarios and all possess high confidence levels.

  • Risk of death, injury, ill-health, or disrupted livelihoods in low-lying coastal zones and small island developing states and other small islands, due to storm surges, coastal flooding and rising sea level.
  • Risk of severe ill-health and disrupted livelihoods for large urban populations due to inland flooding in some regions.
  • Systemic risks due to extreme weather events leading to breakdown of infrastructure networks and critical services such as electricity, water supply, and health and emergency services.
  • Risk of increases in mortality and disease during periods of extreme heat, particularly of vulnerable urban populations and those working outdoors.
  • Risk of food insecurity and the breakdown of food systems linked to warming, drought, flooding, and precipitation variability and extremes, particularly for poorer populations in urban and rural settings.
  • Risk of loss of rural livelihoods and income due to insufficient access to drinking and irrigation water and reduced agricultural productivity, particularly for farmers and pastoralists with minimal capital in semi-arid regions.
  • Risk of loss of marine and coastal ecosystems, biodiversity, and the ecosystem goods, functions, and services they provide for coastal livelihoods, especially for fishing communities in the tropics and Arctic.
  • Risk of loss of terrestrial and inland water ecosystems, biodiversity, and the ecosystem goods, functions, and services they provide for livelihoods.
  • Many key risks constitute particular challenges for the least developed countries and vulnerable communities, given their limited ability to cope.

Future Risks by Sector

  • Freshwater resources: Risks increase significantly as concentrations increase (robust evidence, high agreement). Renewable surface- and groundwater resources are expected to decrease over the 21st century especially in subtropical dry regions which would intensify competition for water supply (limited evidence, medium agreement).
  • Terrestrial & freshwater ecosystems: Both ecosystems are expected to have a large fraction facing extinction risks during and beyond the 21st century. This is because CC can have an impact on other factors such as pollution, invasive species etc. (high confidence). There is also the risk of abrupt and irreversible regional-scale change in the higher RCP scenarios (medium confidence).
  • Coastal & low-lying areas: Rising sea levels are predicted throughout the 21st century. Coastal and low-lying areas will therefore increasingly experience adverse impacts such as flooding and coastal erosion (very high confidence).
  • Marine systems: Global marine-species redistribution and marine-biodiversity reduction will challenge the sustained provision of fisheries productivity (high confidence). For medium to high RCPs, ocean acidification will cause substantial risks particularly to coral reefs and polar regions (medium – high confidence).
  • Food security & food productions systems:  Major crops will see a negative impact on production without adaptation, however individual locations may benefit (medium confidence). All aspects of food stability are affected by CC, including food access and price stability (high confidence).
  • Urban areas: Urban areas are affected by many CC risks (medium confidence). Risks are amplified for those lacking appropriate infrastructure, those in poor quality housing and in exposed areas (medium confidence).
  • Rural areas: Rural areas are exposed to both near- and long-term risks from CC. These impacts include water availability, supply and food shortages (high confidence).
  • Key economic sectors & services: For economic sectors, other stressors, including population, technology, relative prices etc. will be larger than the impacts of CC (medium confidence). Global economic impacts from CC are very difficult to estimate. The most recent, but still incomplete, estimates predict an increase of ~2 oC would have a negative economic effect of between 0.2 and 2 % of income (medium evidence, medium agreement).
  • Human health: Until mid-century CC will impact human health by exacerbating current health issues (very high confidence). It is expected to increase throughout the 21st century in many regions, especially developing countries with low income (high confidence).
  • Human security: The displacement of people is expected to change due to CC (medium evidence, high agreement). CC can increase violent conflicts in the form of civil war by amplifying well-documented drivers of these conflicts such as poverty and economic shocks (medium confidence).
  • Livelihoods & poverty: Throughout the 21st century CC is expected to reduce economic growth, make poverty reduction more difficult and further erode food security (medium confidence).

Future Surface Temperature Scenarios

The following diagram shows how the Earth’s temperature has changed in the last ~110 years (Part A). Any area with insufficient data was left white and any statistically insignificant temperature change is shown with hatched lines. The second diagram in the figure below (B) shows two of the RCP scenarios and how the world’s average temperature could increase whilst following these scenarios. The blue is considered the ‘best case’ scenario where countries adopt a very strict reduction of greenhouse gas (GHG) emissions whereas the red is a ‘carry on as normal’ scenario. The third part to this figure (C) shows two plots much the same as in part A but the two RCP scenarios have been used to show how the Earth’s surface temperature can change depending on what mitigation techniques are adopted. The percentage temperature increase is taken from the average of the Earth’s temperature from 1986-2001. The key things to note from this figure is how dramatically different the future climate could be and how uneven the warming across the world is (for example, the Northern Hemisphere warms much more than the Southern Hemisphere).

: Observed and projected changes in annual average surface temperature. This  figure informs understanding of climate-related risks in the WGII AR5. It illustrates temperature  change observed to date and projected warming under continued high emissions and under  ambitious mitigation.    Technical details: (A) Map of observed annual average temperature change from 1901 to 2012,  derived from a linear trend where sufficient data permit a robust estimate; other areas are white.  Solid colors indicate areas where trends are significant at the 10% level. Diagonal lines indicate  areas where trends are not significant. Observed data (range of grid-point values: -0.53 to 2.50°C  over period) are from WGI AR5 Figures SPM.1 and 2.21. (B) Observed and projected future  global annual average temperature relative to 1986-2005. Observed warming from 1850-1900 to  1986-2005 is 0.61°C (5-95% confidence interval: 0.55 to 0.67°C). Black lines show temperature  estimates from three datasets. Blue and red lines and shading denote the ensemble mean and  ±1.64 standard deviation range, based on CMIP5 simulations from 32 models for RCP2.6 and 39  models for RCP8.5. (C) CMIP5 multi-model mean projections of annual average temperature  changes for 2081-2100 under RCP2.6 and 8.5, relative to 1986-2005. Solid colors indicate areas  with very strong agreement, where the multi-model mean change is greater than twice  the baseline variability (natural internal variability in 20-yr means) and ≥90% of models agree on  sign of change. Colors with white dots indicate areas with strong agreement, where ≥66%  of models show change greater than the baseline variability and ≥66% of models agree on sign of  change. Gray indicates areas with divergent changes, where ≥66% of models show change  greater than the baseline variability, but <66% agree on sign of change. Colors with diagonal  lines indicate areas with little or no change, where <66% of models show change greater than  the baseline variability, although there may be significant change at shorter timescales such as seasons, months, or days.

Observed and projected changes in annual average surface temperature. This
figure informs understanding of climate-related risks in the WGII AR5. It illustrates temperature change observed to date and projected warming under continued high emissions and under ambitious mitigation.

Future Fishing Scenarios

The final figure in this post shows the possible changes to fishing by the middle of this  century. The plot shows the redistribution of the maximum catch potential for over 1000 fish species caught worldwide, and is compared to the 2001-2010 baseline value. The values calculated here are based upon one of the more extreme RCP scenarios. Coastal regions and seas in north-western Europe and other mid- to high-northern latitudes will see an increase in maximum catch potential as more warm-water species migrate northwards. There will be a sharp decrease in maximum catch in the equatorial regions and around the South Pole with differences being as small as half the expected value of the 2001-2010 mean.

 

Climate change risks for fisheries. (A) Projected global redistribution of  maximum catch potential of ~1000 exploited fish and invertebrate species. Projections compare  the 10-year averages 2001-2010 and 2051-2060 using SRES A1B, without analysis of potential  impacts of overfishing or ocean acidification.

Climate change risks for fisheries. (A) Projected global redistribution of maximum catch potential of ~1000 exploited fish and invertebrate species. Projections compare the 10-year averages 2001-2010 and 2051-2060 using SRES A1B, without analysis of potential impacts of overfishing or ocean acidification.

 The IPCC WG2 also goes into detail about adaptation strategies however these have not been covered in this blog post. For more detail on this I suggest Section C of the Summary for Policy Makers. The third and final report by the Working Group 3 (WG3) has been published, and concentrates on potential mitigation choices – the subject of my next post.

Key Figures From The IPCC’s AR5 Report

What is the IPCC?

The IPCC (Intergovernmental Panel on Climate Change) was set up in 1988 by member governments and established by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP). Its objectives were, and still are, “to assess on a comprehensive, objective, open and transparent basis the scientific, technical and socio-economic information relevant to understanding the scientific basis of risk of human-induced climate change“ (From the Principles Governing IPCC Work). Briefly, the IPCC wants to see how the climate it changing, whether humans are contributing to this change and, if so, how much and what are the impacts on the Earth. The reports that are published every 6 years are based on published scientific research from across the world. Each IPCC report is subdivided into three parts which concentrate on 1) the physical science basis, 2) impacts, adaptation and vulnerability and 3) mitigation of climate change. The most recent report, the 5th (AR5), had its Working Group 1 analysis published in September 2013. It is from this report that the figures I explain in this blogpost originate. To give a sense of scale, AR5 has over 800 contributing scientific authors from over 80 different countries. More than 9000 peer reviewed scientific papers contributed to the reports and over 100,000 comments were made and replied to. In terms of scientific review groups, nothing this comprehensive has been achieved on such a scale in any other discipline. The video below was produced when the Working Group 1 report was published. It gives an overview of the scientific reasoning behind the major statements in the report summary.

Understanding the Terminology

If you have read any news coverage of the AR5 report, or perhaps the ‘Summary to Policy Makers’ you will see it is full of phrases such as ‘extremely likely’ and ‘medium confidence’. These terms all have numerical definitions which are summarised in the figures below, for example, extremely likely has a value of between 95-100% certainty. The values will have been calculated using evidence based on observations, computer models results and scientific expert opinion.

IPCC terms defined

IPCC Confidence Defined

Key Figures in the IPCC AR5 Working Group 1 report

All figures shown below can be found in the Summary to Policy Makers report. All the evidence stated above have been combined and assessed to determine the headline statement of the IPPC AR5 that human contribution to climate change is now extremely likely.

Temperature record of the land, ocean and surface from 1850-2012

SPM: Figure 1a

Figure SPM.1: (a) Observed global mean combined land and ocean surface temperature anomalies, from 1850 to 2012 from three data sets. Top panel: annual mean values, bottom panel: decadal mean values including the estimate of uncertainty for one dataset (black). Anomalies are relative to the mean of 1961−1990.

This first plot is fairly self-explanatory. It shows the temperature records based on observational evidence for the land, surface (air closest to the ground) and oceans combined. For more information about temperature records that go further back in time, my previous post entitled ‘4.5 Billion Years of the Earth’s Temperature’ has figures and explanations that may interest you. The temperature values are shown as relative to the average temperature from 1961-1990. The period from 1961-1990 is defined as a ‘normal period’ which is an average value from a 30 year duration. A normal period must have an accurate representation of the present-day or recent average climate. This period should feature a range of climatic variations, including several weather anomalies (for example, severe droughts or cool seasons). 1961-1990 is the official normal period adopted by the WMO. For more information about how these periods are defined please see here. The top figure shows the temperature values as annual data points but the bottom has been averaged into decadal (10 year) values (the different colour lines showing different data sets used). The longest data set we have is the one in black, the grey shaded areas shows the spread in uncertainty associated with this data set. You can see the spread of the shaded area is larger the further back in time you go, showing how our confidence in our observations has improved as more robust measuring techniques are introduced. The first seven decades (the Industrial Revolution) show almost no trend in temperature (if anything a slight decrease in global values) however temperature rises from the 1920s to the 1950s. A plateau is then observed for a few decades before values dramatically rise to present day values. The last three decades have been warmer than any other decade in the last 150 years.

Surface temperature change from 1901-2012

IPCC SPM: Figure 1b

Figure SPM.1: (b) Map of the observed surface temperature change from 1901 to 2012 derived from temperature trends determined by linear regression from one dataset (orange line in panel a). Trends have been calculated where data availability permits a robust estimate (i.e., only for grid boxes with greater than 70% complete records and more than 20% data availability in the first and last 10% of the time period). Other areas are white. Grid boxes where the trend is significant at the 10% level are indicated by a + sign. For a listing of the datasets and further technical details see the Technical Summary Supplementary Material. {Figures 2.19–2.21; Figure TS.2}

This figure gives more information than the one before by showing where in the world the temperature change is occurring. It is sometimes assumed that the rate of global warming is the same throughout the world, but this is not the case. You can see the most intense warming occurs over large land masses. It should be noted that the areas marked with a + sign show when the temperature change is above 10% of the starting temperature which indicates a relatively significant change. Not all areas of the world are warming however, as the blue indicates in the North Atlantic Ocean, there are also certain parts of Antarctica that are cooling but this is not shown in this diagram. As stated in the figure description, the white regions are where <70% of the total data set is recorded and more than 20% of the total data set is in the first and last time periods. Without this information the exact value of temperature change cannot be calculated. This is not to say scientists do not know if these regions are warming or cooling, but the values calculated are not robust enough to the stated here.

Change in rainfall over land from 1901-2010

IPCC SPM: Figure 2

Figure SPM.2 | Maps of observed precipitation change from 1901 to 2010 and from 1951 to 2010 (trends in annual accumulation calculated using the same criteria as in Figure SPM.1) from one data set. For further technical details see the Technical Summary Supplementary Material. {TS TFE.1, Figure 2; Figure 2.29}

This figure shows the change in rainfall over two periods in the last 110 years. Like the figure before areas of white on the land surface indicates where there is not enough data to be able to calculate a value. By comparing the two figures it is clear that we are much more confident in our values for the second half of the 20th century as there are fewer white gaps. This is due to a much larger network of measurements being taken, including satellite data and ground based stations. Africa and South East Asia received less and less rain throughout the 20th century, whereas Europe and the Americas experienced more. The North West coast of Australia has got wetter but the South and East coasts have got drier (this is particularly important as most of the populations of Australia live on the East Coast). This change in rainfall will have a very large impact on societies across the world, both negative and positive. The IPCC Working Group 2 will publish a report in March 2014 concentrating more on the impacts of climate change for the past, present and future.

Comparison of temperature values calculated using computer model results and measured observations

Figure SPM.6 | Comparison of observed and simulated climate change based on three large-scale indicators in the atmosphere, the cryosphere and the ocean: change in continental land surface air temperatures (yellow panels), Arctic and Antarctic September sea ice extent (white panels), and upper ocean heat content in the major ocean basins (blue panels). Global average changes are also given. Anomalies are given relative to 1880–1919 for surface temperatures, 1960–1980 for ocean heat content and 1979–1999 for sea ice. All time-series are decadal averages, plotted at the centre of the decade. For temperature panels, observations are dashed lines if the spatial coverage of areas being examined is below 50%. For ocean heat content and sea ice panels the solid line is where the coverage of data is good and higher in quality, and the dashed line is where the data coverage is only adequate, and thus, uncertainty is larger. Model results shown are Coupled Model Intercomparison Project Phase 5 (CMIP5) multi-model ensemble ranges, with shaded bands indicating the 5 to 95% confidence intervals. For further technical details, including region definitions see the Technical Summary Supplementary Material. {Figure 10.21; Figure TS.12}

Figure SPM.6 | Comparison of observed and simulated climate change based on three large-scale indicators in the atmosphere, the cryosphere and the ocean: change in continental land surface air temperatures (yellow panels), Arctic and Antarctic September sea ice extent (white panels), and upper ocean heat content in the major ocean basins (blue panels). Global average changes are also given. Anomalies are given relative to 1880–1919 for surface temperatures, 1960–1980 for ocean heat content and 1979–1999 for sea ice. All time-series are decadal averages, plotted at the centre of the decade. For temperature panels, observations are dashed lines if the spatial coverage of areas being examined is below 50%. For ocean heat content and sea ice panels the solid line is where the coverage of data is good and higher in quality, and the dashed line is where the data coverage is only adequate, and thus, uncertainty is larger. Model results shown are Coupled Model Intercomparison Project Phase 5 (CMIP5) multi-model ensemble ranges, with shaded bands indicating the 5 to 95% confidence intervals. For further technical details, including region definitions see the Technical Summary Supplementary Material. {Figure 10.21; Figure TS.12}

This figure has a lot of information and can appear quite complex. The individual graphs show computer model values and real measurement values for different regions of the globe. The yellow boxes are temperature values for the land and the white are for the oceans/seas. There are two different types of model simulations here, one where only natural processes that drive changes in climate are considered (for example solar variability, aerosols from volcanic eruptions etc.) These model runs are shown in purple. There are many different computer models in the world and all will produce slightly different results, which is why the pink lines are shown as shaded areas to show the spread in results, or the uncertainty associated with these models. The pink shaded lines show computer model results where both the natural climate forcings AND human forcing are considered in their runs. For example, these will include fossil fuel emissions, CFC emissions etc. Crucially, in all of the graphs in this figure, the only way for the model results to agree with the measured observations (shown as thin black lines) occurs when both natural and human climate forcings are considered.

Current Radiative Forcing Estimates compared to 1750 values

IPCC SPM: Figure 5

Figure SPM.6 | Radiative forcing estimates in 2011 relative to 1750 and aggregated uncertainties for the main drivers of climate change. Values are global average radiative forcing (RF14), partitioned according to the emitted compounds or processes that result in a combination of drivers. The best estimates of the net radiative forcing are shown as black diamonds with corresponding uncertainty intervals; the numerical values are provided on the right of the figure, together with the confidence level in the net forcing (VH – very high, H – high, M – medium, L – low, VL – very low). Albedo forcing due to black carbon on snow and ice is included in the black carbon aerosol bar. Small forcings due to contrails (0.05 W m–2, including contrail induced cirrus) and HFCs, PFCs and SF6 (total 0.03 W m–2) are not shown. Concentration-based RFs for gases can be obtained by summing the like-coloured bars. Volcanic forcing is not included as its episodic nature makes is difficult to compare to other forcing mechanisms. Total anthropogenic radiative forcing is provided for three different years relative to 1750. For further technical details, including uncertainty ranges associated with individual components and processes, see the Technical Summary Supplementary Material. {8.5; Figures 8.14–8.18; Figures TS.6 and TS.7}

For a specific definition of radiative forcing please read the beginning of my first blog ‘A brief introduction to Global Warming’ but essentially a positive radiative forcing (RF) means a warming of the atmosphere and a negative means a cooling. The figure above shows the contributors to climate change. This figure has been developed from the previous report published by the IPCC in 2008. This new figure now shows how each factor can affect temperature (the second from the left column). For example, the top compound carbon dioxide (CO2) warms the atmosphere directly by being present in the atmosphere however when looking at the methane value (CH4) there are four compounds in the second from left column. This means that not only does methane warm the atmosphere directly but when it reacts with other compounds in the atmosphere and produces water (H20), ozone (O3) or carbon dioxide (CO2) then these also warm the atmosphere. The corresponding colours on the bar to the right show how much of this warming is because of which process. The majority factor being direct warming from methane itself but then warming from ozone (produced whem methane reacts in the atmosphere) also has a large contribution. Aerosols can have both a warming and cooling effect on atmospheric temperatures. In the 5th IPCC report it is now possible to see which types of aerosols warm and which cool and by how much (for more information about aerosols please read by blog ‘A brief Introduction to Aerosols). Our confidence for the RF values are stated in the right column.

Temperature predictions to the year 2100 with different RCP scenarios

IPCC SPM: Figure 7

Figure SPM.7 | CMIP5 multi-model simulated time series from 1950 to 2100 for (a) change in global annual mean surface temperature relative to 1986–2005.

Governments, policy makers and climate scientists have all resolved four different representative concentration pathway (RCP) scenarios to predict the average global temperature leading up to 2100. These four RCP values relate to what the radiative forcing could be by 2100 and are 2.6, 4.5, 6.0 and 8.5 respectively. For example, the RCP 2.6 has a radiative forcing of 2.6 (very similar to today’s values – see graph below) whereas a RCP value of 8.5 has over 3 times the amount of warming by 2100. The figure above shows that there could be a huge difference in global average temperature depending of which RCP scenario the world adopts. To get a sense of perspective, for the RCP 2.6 scenario the world must adopt a very strict reduction of greenhouse gas (GHG) emissions – this is effectively the ’best case scenario’. The RCP 8.5 is a ‘business as usual’ scenario where we make little or no reductions of GHG emissions. It should be noted that we are currently (as a globe) doing slightly worse than the RCP 8.5 scenario due to an increase in power production in developing countries and a failure to strictly reduce current emissions. It is generally agreed that a temperature increase of 4 ⁰C would have significant impacts on global society.

I hope you have enjoyed reading this post, I have certainly tried to cram a lot of information here! For anyone who is interested, one of the lead authors of the IPCC AR5, Prof. Piers Forster, summarised the report in 18 tweets.They are well worth a read and may help to summarise some of the things written in this post. The link to these tweets can be found here.

A brief Introduction to Global Warming

Hello and welcome to my first blog post! I can’t really start without an explanation of how global warming occurs, as this is one of the most fundamental reasons why climate science exists! So here we go…

The Earth’s atmosphere allows life as we know it to exist. Without it, global temperatures would be around 33-35 oC colder. The gases that make up our atmosphere can absorb some of the sun’s energy leading to an increase in temperature. Energy from the Sun reaches the Earth in the form of light and heat. The Earth has the ability to absorb all of this radiation but some is reflected back into space either by the Earth’s surface or by its atmosphere. This process is called the Albedo Effect and without it the Earth would be much warmer. The Earth re-radiates energy at a slightly longer wavelength that can be absorbed by some atmospheric gases. These gases then re-radiate this as thermal energy.

A measure of how strong an effect this re-radiated energy has on the Earth’s temperature is called a gas’ radiative forcing. Radiative forcing is the difference between radiant energy received by the earth and energy radiated back into space, and its units are in watts per meter squared (Wm-2). The gases that contribute most to the greenhouse effect, in terms of their radiative forcing, their lifetimes and also their abundance in the atmosphere include carbon dioxide (CO2), water vapour (H2O) and methane (Ch4). The relationship between temperature and concentrations of these gases is strikingly positively correlated, as the graph below shows. In another blog I plan to explain more about how the Earth’s temperature has changed throughout geological history.

Record of the Earth's temperature and Carbon Dioxide concentrations taken from ice core data in Antarctica.

Record of the Earth’s temperature and carbon dioxide concentrations taken from ice core data in Antarctica.

Almost all atmospheric gases have both natural and anthropogenic (man-made) sources. In fact, for most of the major greenhouse gases natural sources outweigh man-made. Since the Industrial Revolution, however, anthropogenic emissions have been rapidly increasing. The plots below, published by the Intergovernmental Panel on Climate Change (IPCC), show just how high the atmospheric concentrations have risen. It is this increase, or offset from the pre-industrial balance between sources and sinks, that is causing temperatures to rise. For more information on the IPCC and its soon to be released 5th assessment report click here.  Or if you want a more detailed summary of all the aspects of climate change this ‘summary for policy makers’ is really interesting.

Timeseries of Methane (CH4), Carbon Dioxide (CO2) and Nitrous Oxide (N2O) emissionsfor the last 10,000 years.

Time series of Methane (CH4), Carbon Dioxide (CO2) and Nitrous Oxide (N2O) emissions for the last 10,000 years.

Of course natural variability also affects the earth’s climate and can contribute to global warming. Examples of natural variability include variations in the Earth’s orbits (i.e. Milankovitch cycles – more to come in another blog), solar radiation variability, lunar tides and interactions between the oceans and the atmosphere. The world’s scientific community agree that the Earth is currently warming however there is a degree of discussion about how much human impact is contributing to global warming. The IPCC has stated that ‘the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations’. Very likely being classed as a >90% probability.

Thanks for reading what I hope is the first of many blog posts.  Next up I will discuss changes to climate that occur on longer times scales, i.e changes to the Earth’s orbit about that sun.