A report commissioned by the World Bank warns that the planet is currently headed toward a 4° C increase in temperature by the end of this century, “triggering a cascade of cataclysmic changes that include extreme heat-waves, declining global food stocks and a sea-level rise affecting hundreds of millions of people.”
Although the report concludes that current pledges to reduce greenhouse gas emissions will not reduce the predicted 4° rise by much, it also suggests that more agressive action might still hold warming below 2°C — the goal adopted by the international community but one that would still result in serious damage and risks to the environment and human populations.
“The Earth system’s responses to climate change appear to be non-linear,” points out PIK Director, John Schellnhuber. ”If we venture far beyond the 2 degrees guardrail, towards the 4 degrees line, the risk of crossing tipping points rises sharply. The only way to avoid this is to break the business-as-usual pattern of production and consumption.”
The comprehensive, 100-page document summarizes a range of direct and indirect climatic consequences under the current global path for greenhouse gas emissions.
Key findings include:
- Extreme heat waves, that without global warming would be expected to occur once in several hundred years, will be experienced during almost all summer months in many regions. The effects would not be evenly distributed. The largest warming would be expected to occur over land and range from 4° C to 10° C. Increases of 6° C or more in average monthly summer temperatures would be expected in the Mediterranean, North Africa, Middle East and parts of the United States.
- Sea level-rise by 0.5 to 1 meter by 2100 is likely, with higher levels also possible. Some of the most highly vulnerable cities are located in Mozambique, Madagascar, Mexico, Venezuela, India, Bangladesh, Indonesia, the Philippines and Vietnam.
- The most vulnerable regions are in the tropics, sub-tropics and towards the poles, where multiple impacts are likely to come together.
- Agriculture, water resources, human health, biodiversity and ecosystem services are likely to be severely impacted. This could lead to large-scale displacement of populations and consequences for human security and economic and trade systems.
- Many small islands may not be able to sustain their populations.
The report confirms unequivocally that humans are the cause of global warming, and that major changes are already being observed at a time when global mean temperature has risen only about 0.8°C above pre-industrial levels.
While a global warming of 0.8°C may not seem large, the report notes that many climate change impacts have already started to emerge, and the shift from 0.8°C to 2.0°C warming or beyond will pose much larger challenges.
A global mean temperature increase of 4°C approaches the known historic level of change for the planet, which harks back to the last ice age when much of central Europe and the northern United States were covered with kilometers of ice and global mean temperatures were about 4.5°C to 7°C lower. And this contemporary human-induced climate change, the report notes, is occurring over a century, not millennia.
“The world must tackle the problem of climate change more aggressively,” said World Bank Group President Jim Yong Kim. “Greater adaptation and mitigation efforts are essential and solutions exist. We need a global response equal to the scale of the climate problem, a response that puts us on a new path of climate smart development and shared prosperity. But time is very short.”
The full report, Turn Down The Heat: Why a 4°C Warmer World Must be Avoided, is available online.