Still time to save the planet... just
By Catherine Brahic A world that is just 0.5 °C warmer in 2100 than before the industrial revolution is a technical, economical possibility – but only just. If we are lucky in certain assumptions and do everything we can to cap our emissions of greenhouse gases, we might be able to prevent more warming. If we are not so lucky, temperatures are more likely to be around 1.4 °C warmer; and if we are unlucky and do nothing to reduce our emissions, the average global temperature by century end could be as much as 7.7 °C warmer than in 1890. These are the conclusions of one of the most thorough attempts so far to look at where concrete climate policies could leave the world in terms of global warming. In its latest report, published in January 2007, the Intergovernmental Panel on Climate Change (IPCC) said the global average temperature could rise by between 1.1 °C and 6.4 °C by 2100. The 0.5 °C to 7.7 °C estimate is more “realistic” says Detlef van Vuuren of the Netherlands Environment Assessment Agency. This is because, unlike the IPCC, he and colleagues have included in their models different climate policies that could be adopted over the coming century. The “emissions scenarios” used by the IPCC do describe how the world could develop in years to come, in terms of population and economic growth. But they do not take into account any government initiatives – such as the Kyoto protocol – to impose emissions caps. In theory, such initiatives should bring temperatures down. Van Vuuren coordinated the efforts of modelling teams around the world to plug 15 policy scenarios into two simple climate change models. The policy scenarios describe regulatory “futures” that are both technically and economically conceivable. They range from very stringent to very lax, and include things like the EU’s target to reduce its emissions to 20% below 1990 levels by 2020. In the most stringent ones, global emissions peak between 2020 and 2040 then drop to nothing by 2100. In some, the land and oceans actually absorb greenhouse gasses out of the atmosphere by 2100, thanks to policies that encourage the planting of new forests and capture and store the emissions generated by burning biofuels. These extreme scenarios lead to an average warming of 1.4 °C above pre-industrial temperatures by 2100. This figure, however, comes with caveats. “There are a number of uncertainties in our understanding of the climate,” says van Vuuren. “If we turned out to be really lucky, we could see a 0.5 °C rise.” If we are “unlucky” the minimum rise could be as much as 2.8 °C. Van Vuuren says governments should prepare for the worst – this minimum warming of 2.8 °C – and start thinking about what needs to be done in the long-term to prepare for this. Air conditioners, he says, can be built fairly quickly, but coastlines cannot be protected from storm surges overnight. On a positive note, the EU’s adopted 2020 target and considered target of limiting emissions to 80% below 1990 levels by 2050 could achieve the least amount of warming – depending, of course, on what other governments do. Climate modeller Gavin Schmidt of NASA’s Goddard Center for Space Studies in New York says the results will not come as a surprise to climatologists. This may be a more comprehensive set of scenarios than considered previously, he told New Scientist, but the conclusions are not unexpected. “The bottom line is that there is already a commitment to future warming as the planet catches up with current emissions and lags in the system both for the climate and human society,” he says “We have a stock of power plants that are likely to be around for 20 or more years,” explains John Reilly of MIT, who participated in the study. “We have a stock of automobile factories that will continue to operate for some time. We can speed things up, but we can’t shut all of that down overnight.” The final and unavoidable uncertainty, which no computer model can predict, is how much political will there is to speed things up. Van Vuuren says it is too early to say whether the current financial crisis will affect future climate policies. Journal reference: Proceedings of the National Academy of Sciences(DOI: 10.1073/pnas.0711129105) Climate Change – Want to know more about global warming – the science, impacts and political debate?