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The State of Play on Climate Change
I. What is climate change?
Climate refers to the average weather experienced over a long period. This includes temperature, wind and rainfall patterns. The climate of the Earth is not static, and has changed many times in response to a variety of natural causes. Climate change is already happening and represents one of the greatest environmental, social and economic threats facing the planet. The 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 mean sea level. The Earth's average surface temperature has risen by 0.76° C since 1850. Most of the warming that has occurred over the last 50 years is very likely to have been caused by human activities.
Global Average Near-Surface Temperatures 1850 - Apr 2008
Eleven out of the last twelve years rank among the 12 warmest on record. According to the Intergovernmental Panel on Climate Change (IPCC) the strong warming of the last 50 years cannot be explained by natural climate variations alone, but requires the inclusion of the effects of human emissions. Much of the observed rise in sea-level (12 - 22 cm) during the 20th century may be related to this increase in global mean temperatures. In its Fourth Assessment Report (AR4), published in 2007, the Intergovernmental Panel on Climate Change (IPCC) projects that, without further action to reduce greenhouse gas emissions, the global average surface temperature is likely to rise by a further 1.8-4.0°C this century, and by up to 6.4°C in the worst case scenario. Even the lower end of this range would take the temperature increase since pre-industrial times above 2°C - the threshold beyond which irreversible and possibly catastrophic changes become far more likely. Projected global warming this century is likely to trigger serious consequences for mankind and other life forms, including a rise in sea levels of between 18 and 59 cm which will endanger coastal areas and small islands, and a greater frequency and severity of extreme weather events.
II. What drives climate change?
Human activities that contribute to climate change include in particular the burning of fossil fuels, agriculture and land-use changes like deforestation. These cause emissions of carbon dioxide (CO2), the main gas responsible for climate change, as well as of other “greenhouse” gases. The most important greenhouse gases are carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulphur hexafluoride. These are the gases that are covered by the Kyoto Protocol. To bring climate change to a halt, global greenhouse gas emissions must be reduced significantly.
Trends in Atmospheric Concentrations and
Anthropogenic Emissions of Carbon Dioxide
- Up until the last two hundred years, atmospheric CO2 concentration had stayed between 265 parts per million (ppm) and 280 ppm according to analyses of gases obtained from ice cores that reflect the past 10,000 years.
- Atmospheric CO2 concentration at the beginning of the 21st Century is approximately 365 ppm.
- Atmospheric concentrations of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) have increased 31 %, 151 %, and 17 % respectively since the year 1750.
- Humans added more than 270 billion metric tons of carbon (GtC) to the atmosphere since the nineteenth century.
- The natural carbon cycle emits about 60-90 GtC per year, while current levels of human-caused emissions are greater than 6 GtC per year.
- About three-quarters of human emissions of CO2 to the global atmosphere during the past 20 years is due to fossil fuel burning.
III. What are the consequences of climate change?
- Increased warming: As pointed out above, eleven of the last twelve years rank among the warmest years in global surface temperature since 1850. The rate of warming averaged over the last 50 years is nearly twice that for the last 100 years. The average global temperature went up by about 0.74°C during the 20th Century with the warming affecting land more than ocean areas.
- There is more carbon dioxide in the atmosphere: Carbon dioxide is the dominant contributor to current climate change and its atmospheric concentration has increased from a pre-industrial value of 278 parts-per million (ppm) to 379 in 2005. According to one of the world’s leading climate scientists, NASA scientist James Hansen, 450 ppm is the maximum allowable carbon dioxide ceiling. At the current rate of emissions this level could be reached within two to three decades.
- Arctic is warming: Average Arctic temperatures increased at almost twice the global average rate in the past 100 years. Satellite data since 1978 show that the average Arctic sea ice extent has shrunk by 2.7 per cent per decade. Although the total area of ice in September fluctuates from year to year, in the last two decades it has generally declined, almost certainly because of carbon-driven global warming. During the summer of 2007, the ice cap shrank at a record-breaking pace; at its minimum it was almost 39 percent smaller than the average from 1979 to 2000.
Arctic Summer Ice
- Glaciers are melting: Mountain glaciers and snow cover have declined, on average, in both hemispheres, and have contributed to sea level rise by 0.77 millimetres a year from 1993 to 2003. Shrinkage of the ice sheets of Greenland and Antarctica have contributed to a sea level rise of 0.4 millimetres a year between 1993 and 2003.
- Slower natural absorption of CO2: Each year, the oceans and land currently take up about half the carbon dioxide that humans emit into the atmosphere. As oceans warm, they absorb less carbon dioxide, partly because the gas dissolves less readily in warmer water, and partly because warming will reduce the mixing between deep and surface waters that provides nutrients to carbon dioxide-absorbing plankton. And when oceans take up less carbon dioxide, warming will worsen.
- Less snow cover: Snow cover is decreasing in most regions, particularly in spring. The maximum extent of frozen ground in the winter/spring season has decreased by about 7 per cent in the Northern Hemisphere since 1900, and on average rivers that freeze do so some 5.8 days later than a century ago and their ice breaks-up 6.5 days earlier.
- More water, but not everywhere: More precipitation has been observed in the eastern parts of North and South America, northern Europe and northern and central Asia in recent decades. But the Sahel, the Mediterranean, southern Africa and parts of southern Asia have experienced drying. More intense and longer droughts have been observed over wider areas since the 1970s.
- Sea level is rising: The rate of observed sea level rise increased from the 19th to 20th century, and the total 20th century rise is estimated to be 0.17 metre. Geological observations indicate that sea level rise over the previous 2,000 years was far less. The average temperature of the global ocean has increased to depths of at least 3,000 metres.
New Projections Indicate Faster Warming…
- Continued greenhouse gas emissions at or above the current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century.
- The degree of warming depends on the degree of emissions: If carbon dioxide concentrations were stabilized at 550 ppm — double the pre-industrial levels — the average warming expected would likely be in the range of 2-4.5°C, with the best estimate of 3°C, or 5.4°F. A warming of 0.2°C per decade is expected for each of the next two decades for a range of scenarios that do not include deliberate reductions in greenhouse gas emissions.
- Other greenhouse gases contribute to warming and if their combined effect were equivalent to a carbon dioxide level of 650 ppm, the global climate would "likely" warm by 3.6°C, while a level of 750 ppm would produce warming of 4.3°C. Projections depend on factors such as economic growth, population, new technologies and other factors.
...and Greater Consequences
- Warmer global temperatures are already causing profound changes in many of the earth's natural systems. Approximately 20-30 per cent of plant and animal species assessed so far are likely to be at increased risk of extinction if increases in global average temperature exceed 1.5-2.5°C.
- A temperature increase of 3°C during this century would have largely negative consequences for biodiversity ecosystems that produce essential goods and services, such as water and food supply.
- As a result of warmer temperatures, springtime events are occurring earlier, such as increased run-off and peak discharge in many glacier- and snow-fed rivers, "greening" of vegetation and migration and egg-laying by birds. More animal and plant species have also been observed shifting toward higher latitudes.
- More precipitation in the high latitudes: Increases in precipitation are very likely in the high latitudes while decreases are likely in most subtropical land regions.
- Model based estimates for sea-level rise due to ocean expansion and glacier melt by the end of the century (compared to 1989-1999 levels) have narrowed from previous assessments to 18-58 cm. However, larger values cannot be ruled out if recently observed movements of ice sheets were to increase as temperature rises.
- Contraction of the Greenland ice sheet is projected to contribute to sea level rise into the 22nd century and the ice sheet could face complete elimination if global average warming of 1.9-4.6°C is maintained for a millennium. In that case, sea level would rise by up to 7 metres.
The figure below produced by the Stern Review illustrates the range of impacts expected at different levels of warming.
Projected Inpacts of Climate Change
IV. Who and What contributes most actively
to climate change?
Most of the world's greenhouse gas (GHG) emissions come from a relatively small number of countries. The United States, China, and the European Union (EU-25) together accounted for about 50% of global emissions in 2004. The eight largest emitters - the United States, China, the European Union, Russia, India, Japan, Germany and Brazil - accounted for more than 70% of global emissions.
Annual GHG Emissions (2004)
Globally, the primary sources of greenhouse gas emissions are the energy supply sector (26%), industry (19%) and forestry (17%). Agriculture and transportation account for 14% and 13% of total emissions, respectively.
Global Anthropogenic GHG emissions by Sector (2004)
V. What needs to be done?
Reversing the historical trend in emissions growth, and achieving cuts of 25% or more against today’s levels is a major challenge. Costs will be incurred as the world shifts from a high-carbon to a low-carbon trajectory. But there will also be business opportunities as the markets for low-carbon, high-efficiency goods and services expand.
Greenhouse-gas emissions can be cut in four ways. Costs will differ considerably depending on which combination of these methods is used, and in which sector:
• Reducing demand for emissions-intensive goods and services
• Increased efficiency, which can save both money and emissions
• Action on non-energy emissions, such as avoiding deforestation
• Switching to lower-carbon technologies for power, heat and transport
The stabilization of greenhouse gases at levels of 500-550ppm CO2e will cost, on average, around 1% of annual global GDP by 2050.
This is significant, but is fully consistent with continued growth and development, in contrast with unabated climate change, which will eventually pose significant threats to growth. However, stabilization at 500 ppm requires that emissions be held near the present level of 7 billion tons of carbon per year (GtC/year) for the next 50 years, even though they are currently on course to more than double.
Large-scale uptake of a range of clean power, heat, and transport technologies is required for radical emission cuts in the medium to long term. The power sector around the world will have to be least 60%, and perhaps as much as 75%, decarbonised by 2050 to stabilize at or below 550ppm CO2e. Deep cuts in the transport sector are likely to be more difficult in the shorter term, but will ultimately be needed. While many of the technologies to achieve this already exist, the priority is to bring down their costs so that they are competitive with fossil-fuel alternatives under a carbon-pricing policy regime.
A portfolio of technologies will be required to stabilize emissions. It is highly unlikely that any single technology will deliver all the necessary emission savings, because all technologies are subject to constraints of some kind, and because of the wide range of activities and sectors that generate greenhouse-gas emissions. It is also uncertain which technologies will turn out to be cheapest. Hence a portfolio will be required for low-cost abatement, including carbon capture and storage, substituting natural gas for coal, wind and photovoltaic electricity, renewable hydrogen and biological sequestration (forest and agricultural soils management).
Even with very strong expansion of the use of renewable energy and other low carbon energy sources, hydrocarbons may still make over half of global energy supply in 2050. Extensive carbon capture and storage would allow this continued use of fossil fuels without damage to the atmosphere, and also guard against the danger of strong climate-change policy being undermined at some stage by falls in fossil-fuel prices.
A shared global perspective on the urgency of the problem and on the long-term goals for climate change policy, and an international approach based on multilateral frameworks and co-ordinated action, are essential to respond to the scale of the challenge. International frameworks for action on climate change should encourage and respond to the leadership shown by different countries in different ways, and should facilitate and motivate the involvement of all states. They should build on the principles of effectiveness, efficiency and equity that have already provided the foundations of the existing multilateral framework.
International co-operation must cover all aspects of policy to reduce emissions – pricing, technology and the removal of behavioral barriers, as well as action on emissions from land use. And it must promote and support adaptation. There are significant opportunities for action now, including in areas with immediate economic benefits (such as energy efficiency and reduced gas flaring) and in areas where large-scale pilot programs would generate important experience to guide future negotiations.
In sum, it is still possible to avoid the worst impacts of climate change; but it requires strong and urgent collective action. Delay would be costly and dangerous.
VI. Sources
- California Climate Change Portal
- European Commission
- Gateway to the UN System’s Work on Climate Change
- Hansen, James, 2008: Tipping point: Perspective of a climatologist. In State of the Wild 2008-2009: A Global Portrait of Wildlife, Wildlands, and Oceans. W. Woods, Ed. Wildlife Conservation Society/Island Press, pp. 6-15.
- Homer-Dixon, Thomas, 2008."Climate Change, the Artic and Canada: Avoiding Yesterday’s Analysis of Tomorrow’s Crisis"
- Pacala, S. and R. Socolow, 2004."Stabilization wedges: solving the climate problem for the next 50 years with current technologies," Science 305: 5686, p. 968-71.
- Pew Center on Global Climate Change
- Stern Review on the Economics of Climate Change
- UK Department for Environment, Food and Rural Affairs
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