Why Clouds Are the Key to New Troubling Projections on Warming

Why Clouds Are the Key to New Troubling Projections on Warming

SOURCE: Yale e360 DATE: February 5, 2020 SNIP: It is the most worrying development in the science of climate change for a long time. An apparently settled conclusion about how sensitive the climate is to adding more greenhouse gases has been thrown into doubt by a series of new studies from the world’s top climate modeling groups. The studies have changed how the models treat clouds, following new field research. They suggest that the ability of clouds to keep us cool could be drastically reduced as the world warms — pushing global heating into overdrive. Clouds have long been the biggest uncertainty in climate calculations. They can both shade the Earth and trap heat. Which effect dominates depends on how reflective they are, how high they are, and whether it is day or night. Things are made more complicated because cloud dynamics are complex and happen on small scales that are hard to include in the models used to predict future climate. Recent concern about how accurately the models handle clouds has focused on the blankets of low clouds that any international flyer will have seen extending for hundreds of miles below them across the oceans. Marine stratus and stratocumulus clouds predominantly cool the Earth. They shade roughly a fifth of the oceans, reflecting 30 to 60 percent of the solar radiation that hits them back into space. In this way, they are reckoned to cut the amount of energy reaching the Earth’s surface by between 4 and 7 percent. But it seems increasingly likely that they could become thinner or burn off entirely in a warmer world, leaving...
Climate Models Are Running Red Hot, and Scientists Don’t Know Why

Climate Models Are Running Red Hot, and Scientists Don’t Know Why

SOURCE: Bloomberg Green DATE: February 3, 2020 SNIP: There are dozens of climate models, and for decades they’ve agreed on what it would take to heat the planet by about 3° Celsius. It’s an outcome that would be disastrous—flooded cities, agricultural failures, deadly heat—but there’s been a grim steadiness in the consensus among these complicated climate simulations. Then last year, unnoticed in plain view, some of the models started running very hot. The scientists who hone these systems used the same assumptions about greenhouse-gas emissions as before and came back with far worse outcomes. Some produced projections in excess of 5°C, a nightmare scenario. The scientists involved couldn’t agree on why—or if the results should be trusted. Climatologists began “talking to each other like, ‘What’d you get?’, ‘What’d you get?’” said Andrew Gettelman, a senior scientist at the National Center for Atmospheric Research in Boulder, Colorado, which builds a high-profile climate model. “The question is whether they’ve overshot,” said Mark Zelinka, staff scientist at Lawrence Livermore National Laboratory. Researchers are starting to put together a­nswers, a task that will take months at best, and there’s not yet agreement on how to interpret the hotter results. The reason for worry is that these same models have successfully projected global warming for a half century. Their output continues to frame all major scientific, policy and private-sector climate goals and debates, including the sixth encyclopedic assessment by the UN’s Intergovernmental Panel on Climate Change due out next year. If the same amount of climate pollution will bring faster warming than previously thought, humanity would have less time to avoid the worst impacts....
New climate models suggest Paris goals may be out of reach

New climate models suggest Paris goals may be out of reach

SOURCE: Phys.Org DATE: January 14, 2020 SNIP: New climate models show carbon dioxide is a more potent greenhouse gas than previously understood, a finding that could push the Paris treaty goals for capping global warming out of reach, scientists have told AFP. Developed in parallel by separate teams in half-a-dozen countries, the models—which will underpin revised UN temperature projections next year—suggest scientists have for decades consistently underestimated the warming potential of CO2. Vastly more data and computing power has become available since the current Intergovernmental Panel on Climate Change (IPCC) projections were finalised in 2013. “We have better models now,” Olivier Boucher, head of the Institut Pierre Simon Laplace Climate Modelling Centre in Paris, told AFP, adding that they “represent current climate trends more accurately”. The most influential projections from government-backed teams in the US, Britain, France and Canada point to a future in which CO2 concentrations that have long been equated with a 3C world would more likely heat the planet’s surface by four or five degrees. For more than a century, scientists have puzzled over a deceptively simple question: if the amount of CO2 in the atmosphere doubles, how much will Earth’s surface warm over time? The resulting temperature increase is known as Earth’s “climate sensitivity”. That number has been hard to pin down due to a host of elusive variables. Whether oceans and forests, for example, will continue to absorb more than half of the CO2 emitted by humanity is hard to predict. “How clouds evolve in a warmer climate and whether they will exert a tempering or amplifying effect has long been a major source...
Earth warming more quickly than thought, new climate models show

Earth warming more quickly than thought, new climate models show

SOURCE: Phys.org DATE: September 17, 2019 SNIP: Greenhouse gases thrust into the atmosphere mainly by burning fossil fuels are warming Earth’s surface more quickly than previously understood, according to new climate models set to replace those used in current UN projections, scientists said Tuesday. By 2100, average temperatures could rise 7.0 degrees Celsius above pre-industrial levels if carbon emissions continue unabated, separate models from two leading research centres in France showed. That is up to two degrees higher than the equivalent scenario in the Intergovernmental Panel for Climate Change’s (IPCC) 2014 benchmark 5th Assessment Report. A new generation of 30-odd climate models known collectively as CMIP6—including the two unveiled Tuesday—will underpin the IPCC’s next major report in 2021. These include increased supercomputing power and sharper representations of weather systems, natural and man-made particles, and how clouds evolve in a warming world. “We have better models now,” said Olivier Boucher, head of the Institute Pierre Simon Laplace Climate Modelling Centre in Paris. “They have better resolution, and they represent current climate trends more accurately.” A core finding of the new models is that increased levels of CO2 in the atmosphere will warm Earth’s surface more—and more easily—than earlier calculations had suggested. If confirmed, this higher “equilibrium climate sensitivity”, or ECS, means humanity’s carbon budget—our total emissions allowance—is likely to shrink. The French models are the first to be released. But other models developed independently have come to the same unsettling conclusion, Boucher confirmed. “The most respected ones—from the United States, and Britain’s Met Office—also show a higher ECS” than the previous generation of models, he...
The terrible truth of climate change

The terrible truth of climate change

SOURCE: The Monthly DATE: August 1, 2019 SNIP: When the IPCC’s fifth assessment report was published in 2013, it estimated that such a doubling of CO2 was likely to produce warming within the range of 1.5 to 4.5°C as the Earth reaches a new equilibrium. However, preliminary estimates calculated from the latest global climate models (being used in the current IPCC assessment, due out in 2021) are far higher than with the previous generation of models. Early reports are predicting that a doubling of CO2 may in fact produce between 2.8 and 5.8°C of warming. Incredibly, at least eight of the latest models produced by leading research centres in the United States, the United Kingdom, Canada and France are showing climate sensitivity of 5°C or...