The Summary for Policymakers breaks down into five subsections:
- Observed changes in climate and their effects
- Causes of change
- Projected climate change and its impacts
- Adaptation and mitigation options
- The long-term perspective
Observed changes in climate and their effects
The first sentence of the summary report pretty much sets the tone:
“Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice and rising global average sea level.”
“Observational evidence from all continents and most oceans shows that many natural systems are being affected by regional climate changes, particularly temperature increases.”
Here we have a graph detailing the growth in global emissions over the past 35 years, along with a breakdown of the various emission types and sources:
The graph above includes the 6 major greenhouse gases (GHGs):
CO2 - Carbon Dioxide
CH4 - Methane
N20 - Nitrous Oxide
HFCs - Hydrofluorocarbons
PFCs - Perfluorocarbons
SF6 - Sulphurhexafluoride
Causes of Change
“Global GHG emissions due to human activities have grown since pre-industrial times, with an increase of 70% between 1970 and 2004.”
“Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations. It is likely that there has been significant anthropogenic warming over the past 50 years averaged over each continent (except Antarctica)”
“Advances since the Third Assessment Report show that discernible human influences extend beyond average temperature to other aspects of climate. Human influences have: + very likely contributed to sea level rise during the latter half of the 20th century + likely contributed to changes in wind patterns, affecting extra-tropical storm tracks and temperature patterns + likely increased temperatures of extreme hot nights, cold nights and cold days + more likely than not increased risk of heat waves, area affected by drought since the 1970s and frequency of heavy precipitation events. “
Projected climate change and its impacts
“There is high agreement and much evidence that with current climate change mitigation policies and related sustainable development practices, global GHG emissions will continue to grow over the next few decades.”
Table SPM.1. Projected global average surface warming and sea level rise at the end of the 21st century:
There are a couple of interesting points to be made about this table - the use of “emission scenarios” and issues around sea level rise:
Emission Scenarios
First - the use of various “emissions scenarios” can be quite confusing - see Emissions Scenarios - What are they and what do they tell us? for a good introduction to the subject. Also see Chapter 4: An Overview of Scenarios from the Special Report on Emissions Scenarios. Finally, the Synthesis Report itself provides the following details on the various scenarios:
“SRES refers to the scenarios described in the IPCC Special Report on Emissions Scenarios (SRES, 2000). The SRES scenarios are grouped into four scenario families (A1, A2, B1 and B2) that explore alternative development pathways, covering a wide range of demographic, economic and technological driving forces and resulting GHG emissions. The SRES scenarios do not include additional climate policies above current ones. The emissions projections are widely used in the assessments of future climate change, and their underlying assumptions with respect to socio-economic, demographic and technological change serve as inputs to many recent climate change vulnerability and impact assessments.
The A1 storyline assumes a world of very rapid economic growth, a global population that peaks in mid-century and rapid introduction of new and more efficient technologies. A1 is divided into three groups that describe alternative directions of technological change: fossil intensive (A1FI), non-fossil energy resources (A1T) and a balance across all sources (A1B).
B1 describes a convergent world, with the same global population as A1, but with more rapid changes in economic structures toward a service and information economy.
B2 describes a world with intermediate population and economic growth, emphasizing local solutions to economic, social, and environmental sustainability.
A2 describes a very heterogeneous world with high population growth, slow economic development and slow technological change.
No likelihood has been attached to any of the SRES scenarios.”
Sea Level Rise
Second - the sea level rise values given in the above table have come in for a great deal of commentary, since they’re lower than the values given in the Third Assessment Report, released in 2001. For an excellent, detailed discussion of this issue see RealClimate: The IPCC sea level numbers.
Regional Impacts
Although under all scenarios the global average temperature will increase, as shown above, regional impacts will vary:
“Regional-scale changes include: + warming greatest over land and at most high northern latitudes and least over Southern Ocean and parts of the North Atlantic Ocean, continuing recent observed trends + contraction of snow cover area, increases in thaw depth over most permafrost regions and decrease in sea ice extent; in some projections using SRES scenarios, Arctic late-summer sea ice disappears almost entirely by the latter part of the 21st century + very likely increase in frequency of hot extremes, heat waves and heavy precipitation + likely increase in tropical cyclone intensity; less confidence in global decrease of tropical cyclone numbers + poleward shift of extra-tropical storm tracks with consequent changes in wind, precipitation and temperature patterns + very likely precipitation increases in high latitudes and likely decreases in most subtropical land regions, continuing observed recent trends.”
The areas likely to be affected the most strongly include:
- “the Arctic, because of the impacts of high rates of projected warming on natural systems and human communities “
- “Africa, because of low adaptive capacity and projected climate change impacts “
- “small islands, where there is high exposure of population and infrastructure to projected climate change impacts”
- “Asian and African megadeltas, due to large populations and high exposure to sea level rise, storm surges and river flooding. “
(These regional impacts are discussed in more detail on pages 9-12 of the Summary for Policymakers)
Adaptation and mitigation options (ie: “what can be done”)
“A wide array of adaptation options is available, but more extensive adaptation than is currently occurring is required to reduce vulnerability to climate change. There are barriers, limits and costs, which are not fully understood.”
“A wide variety of policies and instruments are available to governments to create the incentives for mitigation action. Their applicability depends on national circumstances and sectoral context for future mitigation efforts.”
Here we have a rather confusing graph illustrating possible reductions in CO2 emissions, by sector:
(“OECD” refers to the Organization for Economic Co-operation and Development - essentially 30 of the worlds top industrialized economies. “EIT” refers to “Economies in Transition” - Central and East European countries and former republics of the Soviet Union that are in transition to a market economy.)
As can be seen from the above graph, the largest savings are in the “Buildings” sector - even with a low price for CO2 more than 5 gigatons of CO2 per year could be saved by 2030. This is not surprising, since currently buildings are responsible for almost 50% of CO2 emissions - both from heating/cooling and manufacturing/construction.
On a sector-by-sector basis the SPM identifies various technologies that could be used to reduce CO2 emissions. For example, for Energy Supply:
“Improved supply and distribution efficiency; fuel switching from coal to gas; nuclear power; renewable heat and power; combined heat and power; early applications of carbon capture and storage”
For Transport:
“More fuel-efficient vehicles; hybrid vehicles; cleaner diesel vehicles; biofuels; modal shifts from road transport to rail and public transport systems; non-motorized transport; land-use and transport planning”
etc. Generally, the report avoids radical or “blue-sky” technological solutions, focusing on straightforward improvements in efficiency and the further development of existing technologies.
The long-term perspective
“Determining what constitutes “dangerous anthropogenic interference with the climate system” in relation to Article 2 of the UNFCCC involves value judgements. Science can support informed decisions on this issue, including by providing criteria for judging which vulnerabilities might be labelled ‘key’.”
The report identifies five long-term “areas of concern”:
“Risks to unique and threatened systems: There is new and stronger evidence of observed impacts of climate change on unique and vulnerable systems (such as polar and high mountain communities and ecosystems), with increasing levels of adverse impacts as temperatures increase further. An increasing risk of species extinction and coral reef damage is projected with higher confidence than in the TAR as warming proceeds. There is medium confidence that approximately 20 to 30% of plant and animal species assessed so far are likely to be at increased risk of extinction if increases in global average temperature exceed 1.5 to 2.5°C over 1980-1999 levels.”
“Risks of extreme weather events: Responses to some recent extreme events reveal higher levels of vulnerability than the TAR. There is now higher confidence in the projected increases in droughts, heat waves and floods, as well as their adverse impacts.”
“Distribution of impacts and vulnerabilities: There are sharp differences across regions and those in the weakest economic position are often the most vulnerable to climate change. There is increasing evidence of greater vulnerability of specific groups such as the poor and elderly not only in developing but also in developed countries. Moreover, there is increased evidence that low-latitude and less developed areas generally face greater risk, for example in dry areas and megadeltas.”
“Aggregate impacts: Compared to the TAR, initial net market-based benefits from climate change are projected to peak at a lower magnitude of warming, while damages would be higher for larger magnitudes of warming. The net costs of impacts of increased warming are projected to increase over time. “
“Risks of large-scale singularities: There is high confidence that global warming over many centuries would lead to a sea level rise contribution from thermal expansion alone that is projected to be much larger than observed over the 20th century, with loss of coastal area and associated impacts. There is better understanding than in the TAR that the risk of additional contributions to sea level rise from both the Greenland and possibly Antarctic ice sheets may be larger than projected by ice sheet models and could occur on century time scales. This is because ice dynamical processes seen in recent observations but not fully included in ice sheet models assessed in the AR4 could increase the rate of ice loss.”
