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Billions to Face 'Deadly Threshold' of Heat Extremes by 2100, Finds Study
By Robert McSweeney
Up to three quarters of the world's population could be at risk from deadly heat extremes by the end of the century, a new study suggests.
Keeping global warming to less than 2°C above pre-industrial levels would limit the number at risk from potentially lethal heatwaves to around half of the global population.
But, as other scientists told Carbon Brief, studies into heat-related deaths have a number of challenges to overcome before their findings can become widely applicable across both developed and developing regions.
Recent decades have seen some stark examples of how devastating heatwaves can be. For example, summer heat extremes caused more than 70,000 deaths across Europe in 2003, close to 11,000 in Moscow in 2010 (from both heat and air pollution) and around 740 in Chicago in 1995.
The new study, published Monday in Nature Climate Change, suggests that the number of people at risk from such deadly heat extremes will rise in the future.
The researchers trawled through the peer-reviewed literature for studies published between 1980 and 2014 about heat-related deaths. This turned up 911 papers that covered almost 2,000 case studies from around the world. Of these case studies, 783 focused on specific heatwave events in specific cities.
Using weather data, the researchers compared the conditions during those 783 events against those during other heatwaves in the same cities that didn't cause deaths. On this basis, they found that the combination of average daily temperature and humidity were the best way to differentiate between lethal and non-lethal events. Co-author Dr. Iain Caldwell, from the University of Hawai'i at Mānoa, explained to Carbon Brief:
"We were able to identify a threshold in temperature and humidity, above which conditions have become lethal in the past—we call this threshold the 'deadly threshold' in our paper."
You can see this in the chart below. The black crosses identify the reported temperature and humidity of lethal heat extremes, while the colored hexagons show the conditions during non-lethal heatwaves. The red line indicates the "deadly" threshold above which all events caused deaths.
Average daily surface air temperature and relative humidity during lethal heat events (black crosses) and during non-lethal heat event of equal duration from the same cities (the red to yellow shading indicates the number of such non-lethal events).Mora et al. (2017)
Overall, the researchers found humans are better able to withstand dry heat—e.g. at 20 percent humidity, heat becomes deadly beyond about 40°C—but as humidity increases, the lethal temperature threshold reduces towards 30°C.
This is "consistent with human thermal physiology," the paper said. In hot and humid weather, the air is already heavily laden with water vapor, so your sweat doesn't evaporate and your body can struggle to shed heat.
In the current climate, around 30 percent of the world's population get 20 or more days per year above the "deadly" threshold.
This percentage is increasing as global temperatures rise, the researchers said, and will rise further through the century—depending on how successfully we cut our carbon emissions.
For example, under the RCP8.5 scenario where emissions aren't curbed, as much as 74 percent of the global population could be exposed to at least 20 days of deadly heat extremes a year by the end of the century.
However, cutting emissions to give a good chance of staying below 2°C of global warming—known as the RCP2.6 scenario—would reduce this percentage to 48 percent. At the moment, our emissions are tracking close to RCP8.5.
The study highlights the importance of cutting emissions to minimize how many people will be put at risk, said Dr. Jeremy Pal, from Loyola Marymount University in Los Angeles. Pal wasn't involved in the study, but co-authored a paper in 2015 about the potential for "unbearable" heat extremes in the Middle East. He told Carbon Brief:
"The study is important because it shows additional strong evidence that climate change, if unmitigated, will result in an increase [of] deadly conditions to humans."
The researchers produced an interactive map of their results, for both the past and the future (see below). You can toggle between different decades and different emissions scenarios in the top right-hand corner. You can also watch a time lapse animation of the changing risk from 1950 to 2100 by clicking on the play icon in the bottom left-hand corner.
The shading indicates the scale of the risk of deadly heat days, from low (yellow) to high (red). Clicking on a location will give you a specific projection for the number of days above the deadly threshold.
The results suggest that tropical countries are likely to be worst affected by deadly extreme heat in the future. The findings were less conclusive for large regions of the world—shaded white—where either there wasn't sufficient data (e.g. North Africa), or the results had high uncertainty (e.g. much of the mid-latitudes).
Despite these gaps in the results, this doesn't mean these regions aren't at risk. One example is Western Europe, noted Caldwell:
"Based on the fact that there have already been severe lethal heat events in Europe in the recent past, I personally believe that the risk in these areas remains high. Fortunately, researchers in Western Europe seem to be developing early warning systems that should warn people when conditions are likely to become deadly."
As global temperatures rise, research on heatwaves and health is likely to become ever more pertinent. Yet, as scientists not involved in the study pointed out to Carbon Brief, there are some challenges that these sort of studies need to overcome.
One is that the bulk of the peer-reviewed literature on heat-related deaths refers to extreme heat in developed countries—particularly Europe and North America. You can see this in the map from the study below.
Map of locations where links between heat and mortality have been documented (red squares) and where specific heat episodes have been included in this study (blue squares).Mora et al. (2017)
By basing their threshold for deadly heat and humidity on the available literature, the study is identifying relationships about heatwave risks from predominantly mid-latitude countries and assuming they are valid in other parts of the world.
"We know these relationships are highly city-dependent, changing due to local infrastructure, economy and lifestyle, amongst other things. Cities in Africa face very different challenges to those in Europe, and what is classed as deadly heat in one may not be the same as in another."
So, an increase in heatwaves will impact cities in European differently from those in Africa, said Mitchell. African cities may fare better in some ways, he added, but worse in others:
"You have two competing effects in Africa. The study might overestimate heatwave risks because African cities are already used to higher heat extremes. But the study might underestimate heatwave risks, because African cities have less capacity to adapt to increases and to forecast them accurately."
The study did have some studies outside the mid-latitudes, noted Caldwell, such as in southern India and southern China. And the temperature-humidity threshold was surprisingly consistent across different latitudes, he added:
"Of course, it would be more ideal to have incorporated data for more tropical areas but we had trouble finding such data. Hopefully this will prompt others to remedy this by collecting more data for those regions."
A second challenge is that the risks posed to health by heatwaves depend on socio-economic factors as well as the climate, said Professor Kristie Ebi of the department of global health at the University of Washington. These include, for example, the extent that people are exposed to heat extremes, how vulnerable they are, and whether they are able to prepare and manage for heatwaves.
In fact, there is evidence that in some parts of the world people are already adapting to worsening heat extremes, said Ebi:
"There is growing literature that sensitivity to heatwaves has declined over recent decades, presumably because of some degree of acclimatization to ever higher temperatures, increasing access to air conditioning and cooling centers, better understanding and communication of the risks of high ambient temperatures, and changing infrastructure to reduce urban heat islands."
Including projections of recent and future changes in exposure and vulnerability would have been a helpful addition to the new study, Ebi added.
Reposted with permission from Carbon Brief.
EcoWatch Daily Newsletter
By Julia Conley
Scientists at the United Nations' intergovernmental body focusing on biodiversity sounded alarms earlier this month with its report on the looming potential extinction of one million species — but few heard their calls, according to a German newspaper report.
The climate crisis is a major concern for American voters with nearly 40 percent reporting the issue will help determine how they cast their ballots in the upcoming 2020 presidential election, according to a report compiled by the Yale Program on Climate Change Communication.
Of more than 1,000 registered voters surveyed on global warming, climate and energy policies, as well as personal and collective action, 38 percent said that a candidate's position on climate change is "very important" when it comes to determining who will win their vote. Overall, democratic candidates are under more pressure to provide green solutions as part of their campaign promises with 64 percent of Democrat voters saying they prioritize the issue compared with just 34 percent of Independents and 12 percent of Republicans.
The climate crisis has become a driving and dividing factor in the political arena in recent years. According to the survey, almost three-quarters of respondents think global warming is happening (though that number varies across party lines) with more than half of registered voters agreeing that it is driven by human activities. As such, six-in-ten voters are worried about the current state of the climate — a marked increase from the last survey conducted in March 2018.
When asked how much they would support different strategies the government could use to reduce air pollution, more than three-quarters agreed that investing in renewable energy research and infrastructure and regulating pollution was a priority, as well as taxing pollution (requiring companies to pay a tax on pollution they emit to encourage a reduction in emissions). A majority of respondents also support more specific policies to reduce carbon pollution and promote clean energy, including a revenue-neutral carbon tax and a fee on carbon pollution that distributes money to U.S. citizens through monthly dividend checks. Furthermore, many support a Clean Power Plan that implements strict carbon dioxide emission limits on existing coal-fired power plants. A majority of voters also say they want policies that address the pollution that causes global warming and reduces pollution investments, regulations and taxes.
Climate change ranks as the 17th most important voting issue and is a more polarizing topic than abortion. So much so, that almost half of registered voters say they would support a president who declared global warming a national emergency if Congress does not act.
A handful of 2020 presidential candidates have put climate change at the forefront of their campaign platform as part of ongoing pressure to combat the effects of climate change. The Green New Deal, unveiled in part by Representative Alexandria Ocasio-Cortez (D-NY) earlier this year is a decade-long plan that will "mobilize every aspect of American society ... to achieve net-zero greenhouse gas emissions and create economic prosperity for all," according to a section of the resolution from her office posted by NPR.
Colorado Senator Michael Bennet, who introduced a plan just a few days ago to combat climate change. In it, Bennet calls for the establishment of a "Climate Bank" to use federal spending to incentivize the private sector to transition to net-zero emissions by 2050. His opponent, Governor Jay Inslee of Washington State, similarly announced a clean energy plan earlier this month dubbed the "100 Percent Clean Energy for America Plan" that would aim to phase out coal over the next decade and require all power production to be emissions-free by 2035.
Former Vice President Joe Biden also threw his name into the running hat but didn't mention climate change in his announcement. His overall stand on the Green New Deal and fossil fuel infrastructure is hazy. His campaign website promises environmental action but does not go into further detail. If elected president, Senator Elizabeth Warren has promised an executive order to ban new fossil fuel extraction leases in federal lands and waters.
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President Donald Trump has agreed to sign a $19.1 billion disaster relief bill that will help Americans still recovering from the flooding, hurricanes and wildfires that have devastated parts of the country in the past two years. Senate Republicans said they struck a deal with the president to approve the measure, despite the fact that it did not include the funding he wanted for the U.S.-Mexican border, CNN reported.
"The U.S. Senate has just approved a 19 Billion Dollar Disaster Relief Bill, with my total approval. Great!" the president tweeted Thursday.
"There was a lot of devastation throughout the state," Governor Mike Parson said at a Thursday morning press conference, as NPR reported. "We were very fortunate last night that we didn't have more injuries than what we had, and we didn't have more fatalities across the state. But three is too many."
georgeclerk / E+ / Getty Images
By Jennifer Molidor
One million species are at risk of extinction from human activity, warns a recent study by scientists with the United Nations. We need to cut greenhouse gas pollution across all sectors to avoid catastrophic climate change — and we need to do it fast, said the Intergovernmental Panel on Climate Change.
This research should serve as a rallying cry for polluting industries to make major changes now. Yet the agriculture industry continues to lag behind.
"The Ministry of Environment, Natural Resources Conservation and Tourism wishes to inform the public that following extensive consultations with all stakeholders, the Government of Botswana has taken a decision to lift the hunting suspension," the government announced in a press release shared on social media.