Global warming is real and will continue, and there’s strong evidence that people are to blame, an international panel of scientists has concluded. Other scientists suggest ways that people might reduce future atmosphere-warming greenhouse-gas emissions and argue that societies will have to adapt to the climate change that’s yet to occur.
“The evidence for warming having happened on the planet is unequivocal,” says Susan Solomon, an atmospheric scientist at the National Oceanic and Atmospheric Administration in Boulder, Colo. “We can see that in rising air temperatures, we can see it in changes in snow cover in the Northern Hemisphere, we can see it in global sea rise,” she says. Solomon and her colleagues on the Intergovernmental Panel on Climate Change (IPCC) released their latest assessment of recent warming trends at a press conference in Paris on Feb. 2.
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The average temperatures at Earth’s surface for 11 of the past 12 years rank among the dozen highest values recorded since the mid-1800s. Over the past 100 years, global average temperature has risen about 0.74°C, the IPCC researchers report. With 90 percent certainty, scientists link that increase to the rising concentrations of carbon dioxide and other heat-trapping greenhouse gases that human activities have released into Earth’s atmosphere.
Carbon dioxide concentrations measured 379 parts per million (ppm) in 2005, far in excess of the fractions inferred from ice-core data representing periods going back 650,000 years. The concentration of atmospheric carbon dioxide is now growing at around 1.9 ppm per year, the largest rate of increase ever measured. Accordingly, scientists suggest in the IPCC report that over the next 20 years, the average global temperature will rise by an additional 0.4°C.
Today, coal and petroleum combustion each account for about 40 percent of global carbon dioxide emissions, says Daniel P. Schrag, a geochemist at Harvard University. The largest use of coal, burning it to generate electricity, produces about 8 billion tons of carbon dioxide each year—”more than any responsible climate change policy can accommodate,” he says in the Feb. 9 Science.
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Strategies to decrease carbon dioxide emissions include reducing energy use, capturing carbon dioxide at its sources and sequestering it, or expanding the application of energy sources that don’t produce the gas. “It’s clear that none of these is a silver bullet,” says Schrag.
However, one promising technique is to lock away the gas by injecting it into seafloor sediments or by pumping it into saline aquifers or old oil and gas fields. In ongoing research, scientists at a handful of test sites sequester only about 1 million tons of carbon dioxide each year, Schrag reports.
Even the most optimistic projections of emissions limits show global greenhouse-gas concentrations rising for the foreseeable future, says Roger Pielke Jr., a policy analyst at the University of Colorado at Boulder. Future climate change is unavoidable, he and his colleagues report in the Feb. 8 Nature. Therefore, they add, adaptation to the warming yet to come will be as essential to climate policy as greenhouse-gas mitigation.
The IPCC is scheduled to address the mitigation of climate change in an April report. In May, the group will issue an assessment of the societal impact of current and future warming and is to suggest how people might best adjust to the change.