Greenhouse gas emissions are on track to cause catastrophic global warming of 4 Celsius by 2070 devastating American agriculture and the earth's ecosystems according to a volume of reports published today by the Royal Society.
Temperature changes of between 4 and 8°C are projected in the summer across various temperate and tropical regions for a global 4°C temperature rise [42]. This suggests that these adaptive capacities might be exceeded, especially in the areas with the larger temperate rises such as the USA, the Mediterranean and many parts of Africa [42]. Many of these studies do not include damage caused by concomitant increases in tropospheric ozone and extreme weather events, and so the estimated adaptive capacities might be over-optimistic. For ecosystems, while adaptation to a 2°C world is considered feasible, the options for adapting, either naturally or with human assistance, to a 4°C world are extremely limited, since at these temperatures few ecosystems would be expected to be able to maintain their current functioning [43].
The failure of Copenhagen and earlier global climate conferences have allowed greenhouse gas emissions to increase at rates higher than the IPCC's worst case estimates before the global economic recession. The recession brought emissions back to worst case levels. Because of the political failures, climate scientists have determined that the stated objective of the Copenhagen conference to keep global temperature increases less than 2 degrees Celsius (about 4 degrees Fahrenheit) is not achievable. Moreover, the scientists warn of catastrophic consequences of the likely temperature increases.
A hellish vision of a world warmed by 4C within a lifetime has been set out by an international team of scientists, who say the agonisingly slow progress of the global climate change talks that restart in Mexico today makes the so-called safe limit of 2C impossible to keep. A 4C rise in the planet's temperature would see severe droughts across the world and millions of migrants seeking refuge as their food supplies collapse.
"There is now little to no chance of maintaining the rise in global surface temperature at below 2C, despite repeated high-level statements to the contrary," said Kevin Anderson, from the University of Manchester, who with colleague Alice Bows contributed research to a special collection of Royal Society journal papers published tomorrow. "Moreover, the impacts associated with 2C have been revised upwards so that 2C now represents the threshold [of] extremely dangerous climate change."
Greenhouse gas emissions are increasing at the rate of the IPCC's worst case scenario, A1FI.
Figure 7.
Projections of global warming relative to pre-industrial for the A1FI emissions scenario, using an ensemble of simulations with the MAGICC SCM tuned against the AR4 GCMs and C4MIP-coupled climate–carbon-cycle models. Dark shading shows the mean ±1 s.d. for the tunings to 19 AR4 GCMs, and the light shading shows the change in the uncertainty range when uncertainties in climate–carbon-cycle feedbacks from C4MIP are included. The horizontal red dashed line marks warming of 3.5°C relative to 1980–2000, which represents 4°C relative to pre-industrial [levels].
This paper presents simulations of climate change with an ensemble of GCMs driven by the A1FI scenario, and also assesses the implications of carbon-cycle feedbacks for the climate-change projections. Using these GCM projections along with simple climate-model projections, including uncertainties in carbon-cycle feedbacks, and also comparing against other model projections from the IPCC, our best estimate is that the A1FI emissions scenario would lead to a warming of 4°C relative to pre-industrial during the 2070s. If carbon-cycle feedbacks are stronger, which appears less likely but still credible, then 4°C warming could be reached by the early 2060s in projections that are consistent with the IPCC’s ‘likely range’.
The consequences of a 4 C (7°F) rise in global temperature will be greater than humans can mitigate or adapt to. A billion people may be driven from their homes by climate change. Large areas, such as the western U.S. and great plains, will be affected by warmer drier temperatures. The wheat belt is forecast to move rapidly north and diminish in area as the climate warms and dries out the plains. Declining agricultural yields will threaten millions, possibly billions with hunger, malnutrition and starvation. The ability of natural ecosystems to support the growing human population will be severely stressed.
...a 4°C world would be facing enormous adaptation challenges in the agricultural sector, with large areas of cropland becoming unsuitable for cultivation, and declining agricultural yields. This world would also rapidly be losing its ecosystem services, owing to large losses in biodiversity, forests, coastal wetlands, mangroves and saltmarshes, and terrestrial carbon stores, supported by an acidified and potentially dysfunctional marine ecosystem. Drought and desertification would be widespread, with large numbers of people experiencing increased water stress, and others experiencing changes in seasonality of water supply. There would be a need to shift agricultural cropping to new areas, impinging on unmanaged ecosystems and decreasing their resilience; and large-scale adaptation to sea-level rise would be necessary. Human and natural systems would be subject to increasing levels of agricultural pests and diseases, and increases in the frequency and intensity of extreme weather events.
In such a 4°C world, the limits for human adaptation are likely to be exceeded in many parts of the world, while the limits for adaptation for natural systems would largely be exceeded throughout the world. Hence, the ecosystem services upon which human livelihoods depend would not be preserved. Even though some studies have suggested that adaptation in some areas might still be feasible for human systems, such assessments have generally not taken into account lost ecosystem services.