Every month, climate scientists make new discoveries that advance our understanding of climate change's causes and impacts. The research gives a clearer picture of the threats we already face and explores what's to come if we don't reduce emissions at a quicker pace.
Our blog series, This Month in Climate Science, offers a snapshot of the month's significant scientific literature, compiled from some of the leading peer-reviewed journals. This edition explores studies published in September 2018. (To get these updates delivered right to your inbox, sign up for our Hot Science newsletter.)
Deep coral reefs, known as mesophotic reefs, may not be as resilient to climate change as previously thought. Studying the 2016 mass bleaching event of the Great Barrier Reef and Coral Sea, researchers found that while bleaching impacts on deep reefs were less intense than those in shallower depths, they were still severe. Accordingly, deep corals may have a limited ability to act as a refuge and provide protection to marine creatures.
Runoff in the Upper Colorado River declined by almost 17 percent between 1916 and 2014, largely due to warming. The Upper Colorado River Basin is an essential water resource for the Southwest.
Scientists found that average temperature increase in U.S. national parks between 1895 and 2010 was double the rate of warming in the country overall. Alaska’s national parks saw the greatest temperature increase.
Researchers discovered that major ecosystem changes occurred during the transition between the ice age and interglacial period, which witnessed warming comparable to that which will occur if emissions continue unabated. Scientists said that without deep emissions cuts, terrestrial ecosystems are at risk of major disruption.
IPCC REPORT ON 1.5°C
The world’s foremost group of climate scientists, the Intergovernmental Panel on Climate Change (IPCC), released a special report in October detailing the differences in impacts the world will see with 1.5°C of warming vs. 2°C. While both levels of temperature rise will produce serious and far-reaching effects, keeping warming to 1.5°C is a much safer threshold than 2°C. Read WRI’s blog posts for more information:
The science of attributing extreme events to human-induced warming continues to advance.Scientists from Stony Brook University analyzed Hurricane Florence in near-real time before it made landfall, and found that climate change was responsible for more than 50 percent of the storm’s increase in rainfall. The hurricane was also about [50 miles] larger in diameter than it would have been without human-induced warming.
Researchers found that the highly active 2017 North Atlantic hurricane season (including Hurricanes Harvey, Irma and Maria) was caused mainly by warmer sea surface conditions in the tropical North Atlantic. We will likely continue seeing more active hurricane seasons, scientists said.
Flood frequency in the Amazon has increased five-fold in recent years. During the first half of the 20th century, there was one flood about every 20 years; from 2000 onwards, one flood occurred every four years. Researchers link the increased flooding to the strengthening of the global Walker circulation, caused in part by Atlantic warming.
Scientists found that limiting warming to 1.5˚C (2.7°F) as opposed to 2˚C (3.6°F) can curb temperature-related mortality in most regions worldwide. Populations in warm climates benefited the most, given the risk of extreme heat and other weather events.
Relatedly, scientists documented how limiting warming to 1.5˚C as opposed to 2˚C can make a large difference for China. They found that under 1.5˚C, the frequency of extreme climate events increases by 16 times, compared to 1976-2005. Under 2˚C, frequency increases 33 times. The extremely hot summer of 2013 would occur almost annually under 2˚C of warming.
Scientists found that human-induced warming has already increased drought risk appreciably in the Caribbean. Climate change contributed 15-17 percent of the severity of the widespread 2013-2016 drought, and around 7 percent of its spatial extent.
Scientists established a link between Arctic warming, sea ice loss and recent weather patterns in North America. Warming is causing extreme weather conditions to stick around longer in the United States, which can lead to droughts, cold spells and heat waves.
Scientists found that 2˚C of warming in Antarctica could lead to the retreat of the Wilkes Subglacial Basin. The basin is the size of Texas and California combined, and could lead to more than 10 feet of sea level rise if it retreats. Scientists also said that some models may underestimate the basin’s potential contribution to future global sea level rise, and perhaps the East Antarctic Ice Sheet, which would raise seas even higher.
A 193-meter-high tsunami near Tyndall Glacier in 2015 can be attributed to climate change. Glacial retreat, combined with thawing permafrost, caused mountain walls to become less stable, which led to a massive rockslide just in front of the glacier. Glacial retreat also produced a body of deep water that fueled the tsunami. These types of glacial tsunamis are troubling because they can lead to flooding downstream.
Scientists said the Arctic’s Vavilov Ice Cap has responded rapidly to a warming climate, accelerating from an average speed of about 2 inches a day to as much as 82 feet a day in 2015! Scientists previously believed ice caps at high latitudes were relatively stable. The rapid collapse of such ice caps could mean glaciers in other polar regions, including in Greenland and Antarctica, are also vulnerable.
Greenhouse Gas Emissions
Scientists found a huge discrepancy between land-use emissions and removals reported by countries and those in models, such as those used in the recent IPCC report. The difference is 4 gigatonnes of carbon dioxide per year for the period of 2005-2014 (GtCO2/yr), the equivalent of 10 percent of total human-caused carbon dioxide emissions over this period. Scientists call for any tracking of progress under the Paris Agreement to reconcile these differences.
While scientists know volcanoes produce carbon dioxide, they’ve never been quite sure of how much. There are direct carbon dioxide measurements for only about one in five sources of volcanic gas emissions; the rest are extrapolated from other measurements. Scientists have now quantified emissions from Iceland’s subglacial Katla volcano, and found that it is one of the largest volcanic sources of carbon dioxide on the planet. Subglacial volcanoes in particular are largely unmeasured because they are difficult to access and there is no visible gas plume. Scientists call for further measurements of subglacial volcanoes to assess whether this is an exception, or whether such volcanoes are an unrecognized contribution to global carbon dioxide emissions.
Policy impacts and technological developments
Large-scale wind and solar farms could have benefits beyond reducing emissions.Scientists found that renewable energy systems in the Sahara could increase surface drag (in the case of wind) and surface reflectivity (in the case of solar panels), which in turn would lead to local warming, increased precipitation and more vegetation. This vegetation could then lead to greater rainfall, creating a positive feedback loop.
Homes in countries that get a lot of sunlight are often painted white to reflect sunlight and stay cool. Material scientists have developed a new paint that can lower surface temperature by 6˚C.Scientists said the costs for cooling could drop up to 15 percent as a result of the paint’s use.
Scientists found that a new European directive incorrectly assumes that wood harvested for bioenergy is a carbon-neutral fuel. In fact, replacing fossil fuels with wood would likely lead to two to three times more carbon in the atmosphere by mid-century per gigajoule of final energy.
As Arctic sea ice melts, more ships will operate in the area. In a surprising finding, scientists reported that emissions from these ships will increase the formation of clouds, resulting in cooling of nearly 1˚C by the end of the century, compared with a shipping-free Arctic. Authors caution that their results should not be seen as an endorsement of shipping in the Arctic as a climate solution: The resulting extraction of oil, gas, minerals and other coastal pollutant sources may counteract the cooling effect.