Ten years after carbon emissions happen, the warming effect is maximized. Methane is even quicker, and far more potent, though it also disappears much more rapidly.

CO2 emissions certainly matter over the long haul but they are important in the short term also, and that means there is some good news. Though China, the world's top polluter, has been allowed to emit unchecked until 2030, the United States is back at early 1990s levels of CO2 emissions and the biggest source of industrial emissions, energy from coal, is back at early 1980s levels, thanks to natural gas.

Climate models will need to be revised. Many simulations focus on the amount of warming caused by emissions sustained over decades or centuries, but the timing of temperature increases caused by particular emission has been largely overlooked. A new paper
in Environmental Research Letters sought to correct that by combining the results from two large modeling studies one about the way carbon emissions interact with the global carbon cycle and one about the effect of carbon on the Earth's climate used by the Intergovernmental Panel on Climate Change.   

"A lot of climate scientists have intuition about how long it takes to feel the warming from a particular emission of carbon dioxide," says  Katharine Ricke
of Carnegie Institution. "But that intuition might be a little bit out of sync with our best estimates from today's climate and carbon cycle models."     

They found that actions taken to avoid emissions today would be felt within the lifetimes of the people who acted, not just by future generations.   

The authors reaffirm that while the warming caused by a single emission reaches a maximum quickly, damage caused by this warming can play out over longer periods, including effects of sea level rise and harm to ecosystems caused by sustained warming.