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

Emissions and temperature

  • 2018 fourth warmest on record: In January, the Berkeley Group announced that 2018 was the fourth warmest year on record, making the last five years the five warmest on record. This was later confirmed by NASA and NOAA.

  • U.S. emissions rose in 2018: A new analysis by the Rhodium Group provides a preliminary estimate for 2018 carbon dioxide emissions in the U.S. After three years of decline, they find that emissions rose sharply by 3.4 percent, constituting the second largest annual increase in the last two decades.  Transportation contributed the most overall to the increase.

  • Rising permafrost temperatures: Permafrost is typically at or below 0˚C, but given human-induced warming, permafrost temperatures have been rising. Using data from a network of permafrost measurements around the globe, scientists have found that between 2007 and 2016 ground temperatures of permafrost rose by about 0.3˚C (0.5˚F). Warming increases the likelihood of permafrost degradation and the release of the organic carbon and methane it stores.

  • China’s methane emissions on the rise: China emits more anthropogenic methane emissions than any other country, largely as a result of coal mining. Despite the enactment of regulations in 2010 to drain and use methane that has been trapped in mines, methane emissions continue unabated, and are now rising by about 1.1 million metric tons per year from 2010 to 2015. The authors suggest that the regulations have had no discernible impact.

Ocean behavior

  • 2018 sees record-warm ocean: Using new analysis for the upper 2 thousand meters of the world’s oceans, researchers have found that ocean temperatures were at a record high in 2018. The last five years have been the hottest ocean temperatures on record.  Ocean warming has been accelerating since the 1990s.
  • Ocean’s conveyer belt behaving differently than models suggest: The Atlantic Meridional Overturning Circulation (AMOC) is the ocean’s conveyer belt, which redistributes heat and regulates the climate around the Western Hemisphere. AMOC is thought to be at risk of slowing down as a result of warming, due to glacial melt entering the ocean. Scientists spent 21 months observing the circulation, and found that contrary to model predictions, most of the current overturning, in which water sinks and returns southward, is happening east of Greenland rather than the west. This new data will help improve the models critical for understanding the prospect of further slowdown or even a shutdown of the AMOC.
  • Little Ice Age leaves a mark in the Pacific: It can take over a thousand years for the deep Pacific to adjust to temperature anomalies and, accordingly, it is said to have a very long memoryResearchers recently found that deep in the Pacific are waters that are still adjusting to the decline in temperature experienced during the Little Ice Age in the 16th century. While most of the ocean is warming due to greenhouse gas emissions, the deep Pacific may in fact be cooling as a result.
  • Ocean warming faster than predicted: More than 90 percent of heat trapped by greenhouse gas emissions accumulates in the ocean. Scientists found agreement among multiple lines of temperature measurements that the world’s oceans have been warming about 40 percent faster than the Intergovernmental Panel on Climate Change estimated in the Fifth Assessment Report.


  • Warming to affect your morning coffee: Studying the extinction risk to wild coffee species, researchers have found that at least 60 percent of all coffee species are threatened with extinction. They find that although there are several risks to coffee varieties, including disease and deforestation, climate is a significant threat given projections of longer droughts and the spread of pathogens. If these wild varieties of coffee disappear, it may be more challenging for scientists to create new varieties that can adapt to a warming, drier planet.
  • Climate played a role in asylum applications: Examining data on asylum applications for 157 countries, researchers find that climatic conditions contributes to more severe drought and greater armed conflict, and was associated with asylum applications between 2011 and 2015. This was particularly true for western Asian and northern African countries in 2010-2012, which were experiencing political transformations associated with the Arab Spring.
  • Plants’ absorb less carbon dioxideThis month scientists have discovered that as a result of climate-induced changes in soil moisture, the land carbon sink will be reduced. They suggest that any increase in carbon uptake due to carbon fertilization may not continue in the second half of the century, resulting in a rapid rise in carbon dioxide concentrations.
  • Warming and heart defects in babies: Studying various regions of the United States, researchers have found that maternal exposure to heat during the early stages of pregnancy may contribute to a rise in congenital heart defects. The authors say that heat exposure during the early weeks of pregnancy can lead to fetal cell death or interfere with protein synthesis.
  • Electricity use higher in warmer ChinaResearchers project that annual electricity consumption in the Yangtze River Delta will rise by about 9 percent for every 1°C rise in global average temperatures. The authors hope the results can help inform future planning efforts regarding additional grid capacity. Few studies to date have focused on climate impacts on electricity consumption in non-Western countries.


  • Seals, whales and penguins prefer the cold: Surprisingly, species diversity of marine mammals and birds is greatest when seas are cold in temperate latitudes (unlike other species which tend to have greater diversity in the tropics). In a new study, researchers have established a theory why this is the case: they find that birds and warm-blooded predators (such as whales and seals) are more alert in the colder waters and their cold-blooded prey (such as fish) can be sluggish, giving them a hunting advantage. They note that rising ocean temperatures could have negative impacts on mammal and bird populations, changing the balance of species across the globe.
  • Marine heat waves and collapse of star fish population: The sea star wasting disease has created an epidemic for more than 20 sea star species ranging from Alaska to Mexico. Scientists have found that peak declines of a common sea star species, which has disappeared across the majority of its range, occurred at the same time as warm anomalies in sea surface temperatures. They suggest that the widespread decline of the species could lead to cascading ecosystem impacts.
  • Krill migrating south: Researchers have found that the distribution of krill, which forms the base of the food chain, has declined in their northern ranges in the past 90 years, and populations are becoming more concentrated towards Antarctica in response to warming waters. The authors note that the changing distribution is already affecting the food web.


  • Antarctic sea ice already has a bad record for 2019: The National Snow and Ice Data Center documented that Antarctic sea ice extent was only 5.5 million square kilometers (2.1 million square miles) on January 1, 2019. This is the lowest extent of sea ice on that date for the 40-year old satellite record. They also found that the rate of ice extent loss for December 2018 was the fastest in the satellite record.
  • Six-fold increase in Antarctic ice loss: Using satellite record data, scientists estimate ice mass loss from the Antarctic Ice Sheet has rapidly accelerated over the last four decades – from roughly 40 billion tons per year in 1979–1990 to about 252 billion tons a year in 2009–2017. The ice loss was greatest where there was an influx of warm waters. The scientists estimate the contribution of Antarctic ice to global sea level rise averaged 3.6 mm per decade with a cumulative 14 mm since 1979. The researchers warn that there could be more ice shelves exposed to warm waters than previously thought, especially in East Antarctica, which could contribute multimeter sea level rise if climate change continues unabated.
  • Beneath the surface of Thwaites Glacier: The Thwaites Glacier in the Antarctic Ice Sheet is prone to rapid retreat and is a significant contributor to sea level rise. Researchers have now found a large underwater cavity, two-thirds the size of Manhattan, which used to contain 14 billion tons of ice, but much of it has melted in just three years. The presence of a cavity like this allows for warm waters to get further under the glacier. The scientists suggest that models are underestimating how quickly the glacier is losing ice.
  • Tipping point crossed in Greenland: Past research has focused on sea ice loss from glaciers exposed to the ocean, known as marine-terminating outlet glaciers, on the southeast and northwest of Greenland. Researchers have now found that the largest acceleration of recent ice loss came from southwestern Greenland, which does not have as many marine-terminating glaciers. The authors suggest that one or more tipping points or thresholds have been crossed since the beginning of the millennium, which has triggered the rapid deglaciation. They warn that southwest Greenland would become a major contributor to sea level rise in the future with continued warming.
  • Methane from Greenland’s melt: Methane is a greenhouse gas 28 times more powerful at trapping heat than carbon dioxide. Scientists have now found that methane being produced below the Greenland ice sheet -- from inorganic and ancient organic carbon buried beneath the ice -- is being released into the water during the melt season. The authors suggest that methane leaks from glacier melt has been underappreciated and should be incorporated into efforts to estimate Earth’s methane budget.
  • Loss of ice cover on lakes: To date there has not been a comprehensive large-scale assessment of ice loss of lakes. Researchers have now documented 14,800 lakes that are vulnerable to ice-free winters in the Northern Hemisphere. This number climbs to 35,300 with 2˚C of warming, impacting up to 400 million people, given their reliance on the ice for fish harvest, transportation, recreation, cultural traditions and other services.