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 April 2019. (To get these updates delivered right to your inbox, sign up for our Hot Science newsletter.)


  • Climate change driving economic inequality: Scientists found that over the last few decades, warming has substantially decreased economic growth in many poorer countries located in warmer climates, and increased economic growth in wealthier countries in cooler climates. The authors found that per capita income inequality between the poorest and wealthiest countries is 25% larger than it would be in the absence of human-induced warming. It should be noted that the study largely focused on median losses between 1961 and 2010, rather than decadal trends during this 50-year period.
  • Alarming rates of forest loss: Global Forest Watch data revealed the world lost 12 million hectares of tropical tree cover in 2018, the fourth-highest annual loss since record-keeping began. Forest decline has significant implications for the global carbon sink, among other impacts.
  • Disappearing cloud forests: Researchers modeled climate impacts to tropical cloud forests and found that up to 80%of them will dry or shrink in the next 25-45 years. In Mexico, Central America, the Caribbean, Northern South America and parts of Southeast Brazil, 100% of cloud forests will be affected. Tropical cloud forests harbor some of the highest levels of biodiversity and provide rich ecosystem services, such as providing water and habitat.
  • Reefs reeling: The Great Barrier Reef experienced unprecedented back-to-back heat-induced bleaching events in 2016 and 2017. A new study found that coral larvae declined by 89%, dramatically impairing the reef’s recovery.
  • Marine species more susceptible to warming: One study found that marine species have higher sensitivities to warming than land-based ones. Local extinctions were twice as high among marine species as terrestrial species.
  • Emperor penguin populations plummet: Researchers documented “almost total breeding failure” of the world’s second-largest emperor penguin population, located in Halley Bay, over the last three years. While there has been variability in breeding success from year to year, this period of prolonged breeding failure is unprecedented. The breeding failure coincided with extreme weather, including the strongest El Niño in the last six decades, as well as record-low sea ice cover and early ice break up. Interestingly, a southern colony’s penguin population increased at the same time, suggesting some of the penguins from Halley Bay may have migrated there in pursuit of more favorable conditions.
  • More dead zones:  Scientists looked at historical trends in U.S. waterways and found that annual precipitation, as well as extreme rainfall and warmer spring temperatures, are driving “dead zones” and algal blooms. Extreme precipitation can increase agricultural runoff, leading to greater nitrogen pollution in waters.
  • Impacts of concurrent extremes: Many studies look at extreme events like droughts and heatwaves individually. However, sometimes they occur at the same time. A new study used a technique to examine concurrent climate extremes and identifies vulnerable wheat-producing regions of the world that could experience concurrent heat stress and droughts. Specifically, they found a close interlinkage between drought and heat stress in Australia, Canada, the EU and the United States. This is important because extremes can lead to further yield losses and market shocks.


  • Rapid Antarctic melt: The Ross Ice Shelf takes up about a third of Antarctica’s total ice shelf area. Scientists found that a part of the shelf that is particularly important for its overall stability is melting 10 times faster than the shelf average.
  • Antarctic ice loss could slow: After ice breaks apart, the solid earth rebounds to some degree, much like “a mattress rises after someone gets out of bed.” Scientists found that in the very long term – 350 years into the future – this mechanism will slow the retreat of the Thwaites Glacier in Antarctica by about 38 percent. However, glaciologists caution that there are many other factors fueling the Antarctic ice sheet’s disintegration.
  • Exponential ice loss in Greenland: Studying data from 260 glaciers on the Greenland Ice Sheet from 1972 to 2018, scientists found that mass ice loss increased six-fold since the 1980s. They also found that sea level rose 13.7 millimeters since 1972, with about half of the increase occurring in just the last eight years.
  • Melting Arctic will be costlyResearchers found that melting Arctic permafrost and changes in surface reflectivity will cause $67 trillion in economic losses even if countries’ climate commitments are implemented. Limiting temperature rise to 1.5 degrees C to 2 degrees C (2.7 to 3.6 degrees F) decreases the losses to  $24.8 trillion and $33.8 trillion, respectively.
  • Glacier melt fueling more sea level rise than previously thought: Researchers found that sea level rise from melting glaciers may be greater than previously estimated. Ice loss from glaciers currently contributes 25 to 30 percent of observed sea level rise, and glaciers in some mountain ranges could disappear altogether this century.
  • Disappearing European Alps: Modelers found that if the world limits temperature rise to 1.5-2 degrees C, the European Alps will lose about half of its ice by mid-century. If emissions continue unabated, glaciers in this region will decline by 94% by the end of the century.
  • Melting glaciers in World Heritage sites: Researchers modeled climate impacts to 19,000 glaciers in World Heritage sites, and found that 33 to 60 percent of their ice volume could be lost by the end of the century.


  • Carbon dioxide concentrations higher today than in last 3 million years: Scientists have now established that carbon dioxide concentrations are unprecedented over the past 3 million years. The authors stated that failure to limit global temperature rise to well below 2 degrees C will force Earth “beyond climatic conditions experienced during the entire current geological period.”
  • Warming may be greater than expected: Scientists previously assumed that doubling the world’s pre-industrial carbon dioxide levels would cause 2-4.5 degrees C of warming. However, Science reported that the latest models developed for the next Intergovernmental Panel on Climate Change (IPCC) assessment found that this concentration of carbon dioxide would lead to 5 degrees C of warming or more. If this preliminary analysis proves to be correct, climate impacts would be even more severe for rising concentrations of carbon dioxide than previously thought.
  • Underestimated emissions from Canadian oil sands: Using aircraft measurements, scientists found that annual emissions from Canadian oil sands’ surface mining operations are 64% higher than previous data suggests, and that emissions from the Canadian oil sands overall are 30% higher. The authors said that greenhouse gas inventory guidelines may need to be updated.
  • Permafrost emissions higher than previously assumed: Nitrous oxide is a potent greenhouse gas. Scientists have long assumed that melting permafrost emits carbon dioxide and methane, but only negligible amounts of nitrous oxide. Flying over permafrost on the north slope of Alaska, scientists found nitrous oxide emissions in August—just one month—were equal to the upper limit of previously assumed annual nitrous oxide emissions for the region.
  • Massive plastics emissions: The production of plastics has quadrupled over the last 40 years. A new study showed that without strategies to aggressively reduce plastic consumption, the life cycle emissions of plastics will grow from 1.7 GtCO2e in 2015 to 6.5 GtCO2e by 2050. For reference, the entire United States emitted 5.8 GtCO2e in 2016.
  • Emissions impact of U.S. multinational foreign affiliates: Researchers have for the first time assessed the emissions associated with U.S. multinational enterprise foreign affiliates, which operate beyond the borders of the United States. They found that the carbon footprint of such operations ranks as the 12th top emitter globally, on a scale similar to Australia or the United Kingdom.


  • Why does the ocean sequester carbon? Scientists researched ways the ocean sequesters carbon dioxide and identified a “particle injection pump,” a series of biological and physical processes that move carbon through ocean mixing or via animals. This newly identified “pump” sequesters as much emissions as the well-established gravitational pump. This is a significant scientific breakthrough because previous known mechanisms like the gravitational pump could only partially explain ocean carbon storageAnother study published this month suggests that ocean carbon storage will decline due to warming.

Extreme Weather

  • Warming increased odds of Hurricane Maria’s rains: Scientists studied more than 60 years of precipitation data and found that Hurricane Maria led to the largest amount of rainfall over Puerto Rico since at least 1956. They said that warming made this kind of severe precipitation almost five times more likely to occur.