A World Without Clouds

A World Without Clouds

SOURCE: Nature and Quanta Magazine DATE: February 25, 2019 SNIP: … A picture emerged of a brief, cataclysmic hot spell 56 million years ago, now known as the Paleocene-Eocene Thermal Maximum (PETM). After heat-trapping carbon leaked into the sky from an unknown source, the planet, which was already several degrees Celsius hotter than it is today, gained an additional 6 degrees. The ocean turned jacuzzi-hot near the equator and experienced mass extinctions worldwide. On land, primitive monkeys, horses and other early mammals marched northward, following vegetation to higher latitudes. The mammals also miniaturized over generations, as leaves became less nutritious in the carbonaceous air. Violent storms ravaged the planet; the geologic record indicates flash floods and protracted droughts. As Kennett put it, “Earth was triggered, and all hell broke loose.” The PETM doesn’t only provide a past example of CO2-driven climate change; scientists say it also points to an unknown factor that has an outsize influence on Earth’s climate. When the planet got hot, it got really hot. Ancient warming episodes like the PETM were always far more extreme than theoretical models of the climate suggest they should have been. Even after accounting for differences in geography, ocean currents and vegetation during these past episodes, paleoclimatologists find that something big appears to be missing from their models — an X-factor whose wild swings leave no trace in the fossil record. Evidence is mounting in favor of the answer that experts have long suspected but have only recently been capable of exploring in detail. “It’s quite clear at this point that the answer is clouds,” said Matt Huber, a paleoclimate...
How clouds complicate global warming

How clouds complicate global warming

SOURCE: Cosmos Magazine DATE: July 2, 2018 SNIP: Clouds are wispy evanescent things, beloved of poets and daydreamers. They may also determine whether civilisation as we know it survives the 21st century. Depending on how clouds react to global warming, they could cool or cook the planet. But, so far, we haven’t been able to predict which way they will swing. That’s a big problem for our ability to prepare for what’s coming. At issue is climate sensitivity, which measures how much the temperature changes if the amount of carbon dioxide (CO2) in the atmosphere doubles. In 2014 the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) estimated this number somewhere between 1.5 and 4.5°C. This huge range comes down almost entirely to the effect of clouds. By amplifying warming or reining it in, clouds could make the difference between a 2°C increase – where sea levels rise a metre or more and deadly heatwaves are predicted – and a truly catastrophic 4.5°C – which, according to the IPCC, means widespread extinctions, global food supplies at risk and many parts of the planet too hot to live in. [Fascinating article, I recommend reading the whole...
Scientists have beaten down the best climate denial argument

Scientists have beaten down the best climate denial argument

SOURCE: The Guardian DATE: December 18, 2017 SNIP: A new study published in Nature by Stanford scientists Patrick Brown and Ken Caldeira found that so far, the global climate models that best simulate the Earth’s global energy imbalance tend to predict the most future global warming. These results suggest the ECS is around 3.7°C. This is higher than the previous best estimate of 3.1°C, and if correct, would shrink our carbon budget by about 15%. The study found that the biggest contributor to the difference between the accurate and inaccurate models was in how well they simulated cloud changes. And while it’s just one study, several prior papers arrived at similar conclusions. For example, a 2010 study published in the Journal of Climate found that climate models that most accurately simulate recent cloud cover changes in the east Pacific point to an amplifying effect on global warming and thus a more sensitive...
Sunnier Skies Driving Greenland Surface Melt

Sunnier Skies Driving Greenland Surface Melt

SOURCE: Climate Central DATE: June 28, 2017 SNIP: In the past two decades, the Greenland ice sheet has become the biggest single contributor to rising sea levels, mostly from melt across its vast surface. That surface melt is, in turn, driven mostly by an uptick in clear, sunny summer skies, not just rising air temperatures, a new study finds. While some of the water Greenland is flushing out to sea comes from warming ocean waters lapping away at the glaciers that drain the ice sheet, most is due to the melt across its surface during the summer. Stefan Hofer, a PhD candidate at the University of Bristol in England, and his colleagues looked into what the main drivers of that surface melt were, in particular the effect of cloud cover on melt. In satellite data spanning the past two decades, they saw a significant decrease in cloud cover over Greenland starting in the mid-90s, which would mean more sunlight was falling on the ice and driving melt. Climate models the team used suggest that every 1 percent reduction in cloud cover leads to another 27 gigatons of melt (the U.S. uses about 1.3 gigatons of water per day, according to data from NASA and the U.S. Geological Survey). That sensitivity to cloud cover was “pretty astounding,” William Colgan, a senior researcher with the Geological Survey of Denmark and Greenland who wasn’t involved in the study, said in an...
Climate models have underestimated Earth’s sensitivity to CO2 changes, study finds

Climate models have underestimated Earth’s sensitivity to CO2 changes, study finds

SOURCE: Yale News DATE: April 7, 2017 SNIP: A Yale University study says global climate models have significantly underestimated how much the Earth’s surface temperature will rise if greenhouse gas emissions continue to increase as expected. Yale scientists looked at a number of global climate projections and found that they misjudged the ratio of ice crystals and super-cooled water droplets in “mixed-phase” clouds — resulting in a significant under-reporting of climate sensitivity. The findings appear April 7 in the journal Science. Equilibrium climate sensitivity is a measure used to estimate how Earth’s surface temperature ultimately responds to changes in atmospheric carbon dioxide (CO2). Specifically, it reflects how much the Earth’s average surface temperature would rise if CO2 doubled its preindustrial level. In 2013, the Intergovernmental Panel on Climate Change (IPCC) estimated climate sensitivity to be within a range of 2 to 4.7 degrees Celsius. The Yale team’s estimate is much higher: between 5 and 5.3 degrees Celsius. Such an increase could have dramatic implications for climate change worldwide, note the...