Human activities are the cause of this century's record warm years, according to a study in the journal Scientific Reports.
"We find that individual record years and the observed runs of record-setting temperatures were extremely unlikely to have occurred in the absence of human-caused climate change," the authors say. "These same record temperatures were, by contrast, quite likely to have occurred in the presence of anthropogenic climate forcing."
The study, written before the release of 2015 temperature data, put the odds between 1 in 770 and 1 in 10,000 that 13 of the 15 warmest years spanning from 2000 to 2014 happened without human influence (subscription). With the inclusion of 2015 temperature data, the group's computer simulations widened those odds to between 1 in 1,250 and 1 in 13,000, lead author Michael Mann, a professor of meteorology at Pennsylvania State University, told Reuters.
"Climate change is real, human-caused and no longer subtle--we're seeing it play out before our eyes," Mann said.
Mann and his co-authors ran statistical analyses of real-world measurements and comprehensive computer simulations of the climate system to distinguish human-caused climate change from natural climate variability, such as that triggered by volcanic eruptions and shifts in the sun's output.
"2015 is again the warmest year on record, and this can hardly be by chance," Stefan Rahmstorf, a co-author from the Potsdam Institute of Climate Impact in Germany, said. "Natural climate variations just can't explain the observed recent global heat records, but man-made global warming can."
Study: Low Electricity Costs and Low Emissions Not Mutually Exclusive
A new study by National Oceanic and Atmospheric Administration (NOAA) and University of Colorado Boulder researchers in the journal Nature Climate Change finds that the United States could reduce carbon dioxide emissions from electricity generation (using future anticipated costs for wind and solar) by more than 75 percent relative to 1990 levels by 2030 at approximately the same cost as 2012. The key? Using new high-voltage power lines to move renewables nationwide, eliminating the need to add new fossil fuel storage capacity.
"What the model suggests is we can get a long way, and wind and solar and natural gas can be a bridge," said Christopher Clack of the Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder. "There is a path that could be possible to achieve those goals, and it doesn't necessarily need to drive up costs."
Using NOAA's high-resolution meteorological data, the researchers built a model to evaluate future cost, demand, generation, and transmission scenarios and found that with improvements in transmission infrastructure, the wind and the sun could supply most of the nation's electricity at costs comparable to today's.
"The model relentlessly seeks the lowest-cost energy, whatever constraints are applied," Clack said. "And it always installs more renewable energy on the grid than exists today."
In the expected future scenario--in which renewable energy costs continue to fall while natural gas costs rise--the model predicted that the power sector could cut emissions 78 percent compared with 1990 levels at an electricity cost of 10 cents per kilowatt-hour, up from 9.4 cents in 2012 (subscription). That finding is predicated on creation of a new high-voltage direct-current (HVDC) transmission grid, which according to the authors lowers the chance of energy losses, reducing utilities' need to amass reserves of excess capacity through natural-gas-powered generators.
"With an "interstate for electrons,' renewable energy could be delivered anywhere in the country while emissions plummet," said Alexander MacDonald, co-lead author and former director of NOAA's Earth System Research Laboratory. "An HVDC grid would create a national electricity market in which all types of generation, including low-carbon sources, compete on a cost basis. The surprise was how dominant wind and solar could be."
Update to Social Cost of Carbon Unnecessary
A new interim report from the National Academies of Sciences, Engineering and Medicine suggests that there is little benefit to updating estimates of the social cost of carbon in the near term. Written by a 13-member expert panel, the report recommends ways to change federal technical support documents on the social cost of carbon to enhance estimates.
"We recommended against a near-term update to the social cost of carbon" based off the IPCC report's finding, said Richard Newell of Duke University. Newell co-chaired the panel, which includes Sanford School Professor and Nicholas Institute for Environmental Policy Solutions Faculty Fellow Billy Pizer.
To set an efficient market price on carbon emissions, it's helpful to know the social cost of those emissions--that is, the estimate of the economic damages (in dollars) associated with an increase in carbon dioxide emissions, usually one metric ton, in a given year. The last revised estimate, in 2015, was $36 per metric ton of carbon dioxide.
The Climate Post offers a rundown of the week in climate and energy news. It is produced each Thursday by Duke University's Nicholas Institute for Environmental Policy Solutions.