Every month, climate scientists make new scientific 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 new 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. To get these updates delivered right to your inbox, sign up for our Hot Science newsletter.

This edition explores studies published in July 2018. While it is not meant to be comprehensive, it provides an overview of the latest scientific revelations, including overlooked problems and potential solutions.

Before providing a summary of recent developments in the scientific literature, we felt compelled to take stock of some of the extreme weather developments around the globe. This past month, we have seen the signs of a changing climate. Many of these events are in line with projections of a warming world:

  • Records are being smashed across Europe. Europe had its second warmest June on record in 2018. UK had its third warmest June since record keeping began more than a century ago.
  • This month, NOAA stated that Oman saw its highest minimum temperature at 108.7°F on June 26th, a new Asian record and possibly a world record warm minimum temperature. Also this month, a new record was likely set for the hottest temperature in Africa, at 124°F in Ouargla, Algeria.
  • Japan's weather agency declared a heat wave this past month, and more than 22,000 people were taken to the hospital with heat stroke. The country was also hit by record high rainfall and extensive flooding and mudslides, with thousands of houses damaged and at least 122 lives lost; 5 million people were told to evacuate.
  • In eastern and central Canada, 33 have died due to one of the worst heat waves in decades.
  • In early July, temperatures rose above 110°F in Southern California and electricity demand was so high, due to air conditioning, that the lights went out for tens of thousands.
  • Fires are blazing across the United States, with Yosemite National Park closed at the peak of visitor season. As of the end of July, 98 large fires had already burned 1.2 million acres, with more than 26,000 firefighters working to put them out.
  • Fires are also occurring across Europe. Greece witnessed extensive fires that killed 85 people and injured another 180. Hot conditions have made the fires more challenging to control. Fires are sweeping above the Arctic Circle in Sweden as well, with more than 50 wildfires burning and officials reaching out for foreign assistance.
  • In India, recent drought and resultant crop failures in the Bundelkhand region of India's Madhya Pradesh state has led to significant migration.
  • Many parts of the UK witnessed their driest June on record. As the fields have dried out, they have revealed crop marks from 800 BC to 50 AD, marking old forts and settlements.
  • An iceberg weighing 11 million tons, nearly the length of two football fields, was lodged off a small village in Greenland. If it were to roll over, given its size it could produce large enough waves to wash away parts of the town. The threat forced evacuations.
  • The WMO states that to date, 2018 has been the hottest La Niña year on record.
  • And the list goes on.

These events beg the question: How effective is climate science in understanding the relationship between any given extreme event and human-induced warming? The science of attribution, which attempts to determine whether a particular extreme event is driven by climate change or is within the bounds of normal, is improving, and scientists are also providing faster analysis to help connect the dots between climate change and extreme weather events. For example, this past month:

  • The World Weather Attribution project published a study, released prior to peer review to share the findings more quickly, on the role of climate change in the 2015-2017 drought in the Western Cape of South Africa. The scientists found that the likelihood of such a drought event increased by a factor of three due to anthropogenic climate change. They note that future drought risk increases with further warming.
  • The World Weather Attribution project published another study, also released prior to peer review, that showed that the probability of the 2018 heat wave that northern Europe (across Demark, Finland, Ireland, the Netherlands, Norway and Sweden) is currently experiencing is, on average, more than two times higher today with warming due to human activities.

Overview of Selected Journal Articles


  • Discernible impact of human activities on seasons: Researchers report in Science that it is possible to separate out the influence of human activities vs. natural influences on the Earth's seasons. They specifically studied the temperature of the Earth's troposphere (extending from the surface to 16km at the tropics and 13 km at the poles). Their findings provide new evidence for a statistically significant effect of human activities on the Earth's climate, and find that there is now a greater contrast between the hottest and coldest times of the year.

The Poles

Bad news from the poles. Flickr/National Museum of the U.S. Navy
Bad news from the poles. Flickr/National Museum of the U.S. Navy
  • Ice loss in Nunavut: A study published in the Journal of Glaciology this month finds that between 1999 and 2015 ice coverage in Northern Ellesmere Island, Nunavut, declined about 6 percent (1705 km2). The greatest loss was in ice shelves, which lost 42 percent of their original area. Among marine-terminating ice tongues, 19 of 27 disintegrated.
  • East Antarctic glaciers losing mass: New data are available for East Antarctic, a region in which measurements are difficult to obtain. In Geophysical Research Letters, scientists report that from April 2002 to August 2016, the region lost roughly 18.5 Gt of mass annually (15 percent of its ice flux). The results show unequivocal evidence that the glaciers have been losing mass over the last 15 years.
  • Risk of ice shelf loss in Greenland: Scientists have now discovered that the ice shelf mass balance of a major outlet glacier in Northeastern Greenland, Nioghalvfjerdsfjorden, has been out of equilibrium since 2001. The authors, writing in Nature Communications, note that ice shelf will lose "large parts of its area within a few decades." The glacier is the largest ice shelf in Greenland and the region is a major transportation route for ice discharge into the Nordic Seas, with impacts to large-scale circulation.
  • Revised approach for estimating sea level rise: In Science this month, researchers find that the approach used to understand future sea level rise due to ice sheet sliding over the ground is incorrect. Previously, it was calculated based on a frictional stress between the base of the glacier and its underlying bed. Now, based on a study of 140 glaciers in Greenland, scientists show that instead the speed of flow is determined by the net pressure at the glacier bed, which can lead to more accurate projections of sea level rise.
  • Link between cold winters and Arctic sea ice loss further confirmed: Scientists have recently been debating the relationship between Arctic sea ice loss and cold weather in adjacent continents. Researchers publishing in Science Advances this month show a pattern of colder winters and more frequent cold air outbreaks in Siberia following sea ice loss in the Barents-Kara seas in late autumn. The authors suggest that their results can help reconcile discrepancies among previous studies.
  • Ice sheets more dynamic than we thought: A new study of the Last Glacial Maximum finds that the ice sheets are more dynamic than we thought. Studying the rapid growth in glaciers from 26,500 to 19,000 years ago through piecing together relict coral reefs, the scientists report in Nature that sea level rise was lowered by 17 meters in just 500 years.


  • AMOC to enter two-decade minimum, bringing rapid surface warming: A new study in Nature suggests that the Atlantic Meridional Overturning Circulation (AMOC) will be entering a two-decade minimum in which there will be low levels of heat uptake in the ocean and a rapid period of global surface warming. The authors find that changes to the AMOC since the 1940s are best explained by variability as opposed to human-induced changes. There has been an ongoing debate on RealClimate about this paper since its publishing.

Greenhouse Gas Emissions

  • Carbon budget even smaller: In Nature Geoscience, scientists study the impact of methane releases from permafrost thaw and wetlands on the carbon budget. These emissions – a positive feedback given that emissions rise as temperature increases -- are not adequately represented in most climate models. When they are taken into account, the CO2 emissions budget for 5°C is reduced by 17-23 percent and 9-13 percent for 2°C.
  • Ecosystems less effective at storing carbon: Writing in Science Advances, scientists find that tundra ecosystems are losing their capacity to store carbon. Assessing a four-decade record of CO2 measurements in Barrow or Utqiaġvik, Alaska, they find that carbon is moving through the ecosystem more quickly, with a 13.4 percent decrease in the average carbon residence time. This means that the carbon is escaping more quickly than it had been previously. The carbon cycle of the tundra ecosystem is shifting towards a more "sluggish" boreal ecosystem. The scientists note that carbon release will likely continue and exceed carbon uptake under continued warming.
  • Current GHG Inventory Guidelines underestimate methane emissions: There is a large discrepancy between the 2015 United States' inventory estimate of methane emissions from the oil and gas supply chain and an estimate derived using more advanced methods. The new data was reported in Science, and the authors find that the supply chain emissions were roughly 60 percent higher than the inventory because current estimation methods do not take into account abnormal operating conditions.


Mesophotic reefs like this one are getting warmer as part of human-caused climate change. Flickr/NOAA'S National Ocean Service
Mesophotic reefs like this one are getting warmer as part of human-caused climate change. Flickr/NOAA'S National Ocean Service
  • Fish losing ability to smell: A new study in Nature Climate Change finds that fish will start to lose their ability to detect smells by the end of the century if emissions are not curbed. Fishes' sense of smell is essential for finding food and habitat and for detecting predators, especially when visibility is compromised.
  • Internet infrastructure under threat due to sea level rise: Scientists have found that sea level rise will pose a threat to Internet infrastructure in the United States. They find that more than 4,000 miles of fiber conduit and over 1,000 nodes will be under water in just the next 15 years. New York, Miami and Seattle are at greatest risk.
  • Increased rates in suicide due to warming: A study in Nature Climate Change focuses on the link between increased rates of suicide in Mexico and the United States due to warming. The authors find that suicide rates rise 0.7 percent in US counties and 2.1 percent in Mexican municipalities with a 1°C rise in monthly average temperature. They also assess social media and find that mental well-being is diminished during warmer periods. They suggest that under a high emissions scenario (RCP 8.5), 9,000-40,000 more suicides could occur across Mexico and the US by mid-century. They suggest this figure is equal to roughly one-third the estimated effect of gun restriction laws in the US. Additional health-related stories are the focus of July's PLOS Medicine journal.
  • Significant regional impacts even with low levels of warming: Writing in Nature Geoscience, scientists look back over the past 3.5 million years and find that while there is a low risk of cascading greenhouse gas feedbacks if warming is limited to 2°C, there are substantial regional impacts even with 1-2°C of warming. In the past, such warming has been accompanied by large shifts in climatic zones and altered distributions of ecosystems on the land and oceans. In addition, it has led to significant reductions of the Greenland and Antarctic ice sheets.
  • Flood damage costs estimated under temperature scenarios: Publishing in Environmental Research Letters, researchers have estimated the costs of global flood damage under 1.5 °C and 2 °C. They find a difference of 11 cm of global sea level rise if temperature rises the extra half degree (52 cm under 1.5 °C and 63 cm under 2 °C). This would result in additional losses of US$1.4 trillion per year (0.25 percent of global GDP) without any further adaptation. If warming climbs even further, under a high emissions scenario (RCP 8.5), global flood costs could increase to US$14-27 trillion per year (almost 3 percent of global GDP) without further adaptation.
  • Risk of simultaneous production shocks for maize: A new study in the Proceedings of the National Academy of Sciences finds that simultaneous production shocks for maize could occur across multiple countries if warming is unabated. Only a few countries dominate the production and trade of maize; four countries account for 87 percent of global maize exports. While the likelihood of simultaneous production losses of more than 10 percent is almost zero, the risks of this occurring increases to 7 percent under a 2°C and to 86 percent under a 4°C scenario. The authors suggest that there could be increase instability in trading and pricing, affecting about 800 million people which are most vulnerable to spikes in food market volatility.
  • Monarch butterflies more susceptible to parasites with warming: Monarch butterflies rely upon milkweed to obtain a natural toxin that fights off parasites. However, a new study published in Ecology Letters presents the first evidence of higher CO2 levels reducing the "medicinal properties" in milkweed and as a result the harm from the parasite was higher. Their results show that parasite-host relationships could change in a warming world.
  • Greater population declines in mammals and birds with rapid warming: Reporting in Global Change Biology, scientists present an assessment of warming and land use change on 481 mammals and birds since 1950. They find that population abundance declined for both birds and mammals, with a more pronounced effect in birds, in places where average temperature increased more quickly. Their results find a strong association between rapid warming and population declines.
  • Deep reefs more vulnerable than thought: An article in Science finds that mesophotic reefs, or deep reefs at depths from 30 to 150 meters, are suffering from human-induced warming. These reefs were previously thought to be less vulnerable and reef conservation research had suggested they might provide a refuge for shallow reef species. Instead, the authors suggest that these reefs have as much need for protection as shallow reefs.
  • Impacts can go undetected: In Nature Climate Change, scientists report that while daily rainfall extremes in Australia have been within the range of natural variability, hourly rainfall extremes have been above the range of natural variability. The changes in hourly rainfall extremes cannot be explained by El Niño or changes in seasonality of extremes. Therefore, depending on the scale assessed (in this case daily vs. hourly), impacts can go undetected.
  • High-elevation lakes under threat: In Water Resources Research, scientists find that high- elevation lakes in New England had increased dissolved organic carbon over 1986-2015, in part due to higher temperature and precipitation. Increases in dissolved organic carbon can lead to impacts on water temperature, water clarity, carbon cycling, nutrient and light availability for aquatic organisms, among other impacts.

Policy Design

  • If not designed correctly, mitigation policy could threaten food security: This month's Nature Climate Change includes an analysis of the impacts of climate mitigation efforts on commodity prices for agriculture, dietary energy availability, and the number of people at risk of hunger. The authors find that if a stringent climate mitigation policy, such as a global carbon tax, was applied evenly across sectors and regions, it would have a larger negative impact on hunger and food consumption than the direct impacts of warming by mid-century. Sub-Saharan Africa and South Asia, which are already experiencing food security challenges, would be most vulnerable.
  • Climate awareness associated with mitigation targets: Studying 71 countries and one region, scientists report in Climatic Change that there is a positive association between the number of people in a given country who are aware of climate change and the unconditional targets set by that country. They find that each percentage point that awareness rose was associated with a slightly higher emissions reduction target.