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Climate Change > How much must emissions be reduced?
How much must emissions be reduced?
Determining a limit for the level of greenhouse gases that nature can "cope with" is difficult for several reasons. It is uncertain how the climate system will react to emissions, and we know relatively little about how nature is affected when the climate changes.
Research has shown however that ecosystems and people are affected negatively even if the mean global temperature rises by just a degree or so above the pre-industrial level - which is the expected effect of the cumulative emissions to date.
With a temperature rise of less than one degree, species such as the Bengal tiger and the mountain gorilla are threatened, while a rise of 1-2°C affects coral reefs, coastal wetlands, the availability of food and water for people, etc.
The umbrella organization of the environmental movement on climate issues, Climate Action Network, writes in its position statement (2002) that the global mean temperature increase should be kept less than 2°C above pre-industrial levels, with the temperature being reduced as rapidly as possible after the time of peaking. The rate of change must not exceed 0.1°C per decade in order to allow ecosystems to adapt.
A maximum global mean temperature increase of 2°C above pre-industrial levels is also the goal for the European Union.
The next question is what limit do we need to set on the concentration of greenhouse gases in the atmosphere to meet this target. Here the 2007 assessment report from the IPCC shows that the current level (around 380 ppm carbon dioxide) will mean an increase of around two degrees when equilibrium is reached.
The IPCC shows that to meet the maximum warming target of two degrees above the pre-industrial level with a reasonable degree of confidence, global emissions must peak no later than 2015 and be 50–85 per cent below the 1990 level by the year 2050. See table below.
CO2 conc.
|
CO2 eq conc.
|
Temp. increase1
|
Change in CO2
emissions in 20502 |
Peaking year
for emissions |
ppm |
ppm |
degrees C |
per cent |
year |
350-400 |
445-490 |
2.0-2.4 |
-85 to -50 |
2000-2015 |
400-440 |
490-535 |
2.4-2.8 |
-60 to -30 |
2000-2020 |
440-485 |
535-590 |
2.8-3.2 |
-30 to +5 |
2010-2030 |
485-570 |
590-710 |
3.2-4.0 |
+10 to +60 |
2020-2060 |
570-660 |
710-855 |
4.0-4. |
+25 to +85 |
2050-2080 |
660-790 |
855-1130 |
4.9-6.1 |
+90 to +140 |
2060-2090 |
1 Global mean temperature increase above preindustrial level at equilibrium, using “best estimate” climate sensitivity.
2 In per cent of 2000 emissions.
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