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 October 2018. (To get these updates delivered right to your inbox, sign up for our Hot Science newsletter.)

Impacts

  • No more cheap beer: Scientists found that beer’s main ingredient, barley, is highly susceptible to extreme drought and heat. They predicted yield losses between 3 and 17 percent during extreme event years, compared to average yields from 1981-2010. This could increase beer prices and reduce consumption. During the most severe climate events, scientists found that beer consumption would decline by 16 percent globally, equivalent to annual U.S. consumption, and beer prices would double.

  • World Heritage Sites at risk: Scientists found that of the 49 World Heritage Sites located in low-lying areas of the Mediterranean, 37 of them are at risk of a 100-year flood, and 42 are threatened by coastal erosion. Given future sea level rise, flood risk could increase by another 50 percent.

  • Sea level rise may boost island resilience: Studying the southern Maldives, scientists found that if there is sufficient sediment, high-energy waves occurring with sea level rise could actually build islands up instead of erode them.

  • More frequent extreme precipitation: Modelers projected that the frequency of extreme precipitation events will increase across the entire continental United States over the next century. Most regions can also expect to see an increase in the number of dry days.

  • Collapse of the forest food web: Scientists found that arthropods, lizards, frogs and birds in Puerto Rico’s Luquillo rainforest have declined significantly since the 1970s. They attributed this collapse of the “forest food web” in part to the rainforest warming by 2°C (3.6°F).

  • Disappearing birds in the Andes: Researchers documented the decline of high-elevation bird species in Peru, with some common mountaintop residents disappearing altogether. Tropical mountains contain more species than any other terrestrial ecosystem, and further warming could lead to more extinctions in the Andes. At the same time, lowland bird species may benefit from warmer temperatures, and are expanding their range sizes.

  • Variation of social cost of carbon among countries: The social cost of carbon indicates the expected economic damages resulting from one ton of carbon dioxide. Researchers have taken into account the differences at the country level, and found that countries incurring the largest fraction of global costs are India, China, Saudi Arabia and the United States. The social cost of carbon is used in things like cost-benefit analyses to estimate how much we should be willing to pay today to avoid future damages. These countries stand to pay the highest prices for their emissions because their share of damages is so large. Accordingly, these countries should be willing to pay higher costs of carbon out of pure self interest.

Emissions

  • Lifetime of black carbon shorter than we thought: Black carbon, a potent warming pollutant emitted from coal plants, diesel engines, cookstoves and more, plays an important role in driving climate change and leads to snow and ice melt. Using aircraft measurements over multiple regions, scientists found that the lifetime of black carbon is less than 5.5 days on average, shorter than previous assumptions. However, there are significant regional differences, particularly in the Arctic.

  • Rising methane emissions: While methane emissions had been relatively stable in the late 1990s and early 2000s, they shot up after 2007. A new study found this increase in potent greenhouse gases was predominantly due to microbial sources, such as from wetlands, rice cultivation and ruminant animals, as well as fossil fuel use.

Oceans

  • More plankton in the North Sea: Warmer temperatures are expected to reduce ocean circulation in the North Sea, which could significantly disrupt marine ecosystems. More river water entering the sea may result in greater growth of phytoplankton, which could deplete oxygen near the seabed. Reduced circulation between ocean waters can also disrupt the breeding cycles of some species and increase retention of pollutants.

  • Deep ocean carbon dioxide isn’t staying there: Analyzing pH levels of the deep Southern Ocean over the past 40,000 years, scientists found that carbon dioxide can be released from the deep ocean much more quickly than previously thought, and subsequently transferred to the upper ocean and atmosphere. This process helped end the last ice age, which led to a significant rise in seas and melting of ice sheets. Today’s rise in carbon dioxide emissions is occurring even more rapidly and at a greater scale.

Arctic and Antarctic

  • Phytoplankton blooms from Arctic ice loss: Shrinking ice cover in the Arctic has led to earlier phytoplankton blooms in spring, especially in the Barents and Kara Seas. Such blooms are also expanding northward. This could lead to a mismatch between the timing and location of the blooms and the species that feed on them.

  • More sea ice…for now: One study posited that we will see Arctic sea ice growth in the winter over the coming decades, because thinner ice can grow faster than thicker, insulated ice. However, scientists added that this is only expected through mid-century, and ice will decline after that.

  • Internal variability causes some Arctic sea ice decline: While Arctic sea ice loss is caused in part by human-induced warming, scientists found that internal variability, such as atmospheric circulation patterns, contributed 40-50 percent of the decline over the past 37 years. Researchers argued that such sea-ice sensitivities should be reflected in scientific models.

Temperature change

  • Sticking to 1.5°C: While the Paris Agreement’s goals of limiting global temperature rise to 1.5°C-2°C (2.7°C-3.6°C) relate to long-term average temperatures, scientists have now developed a methodology to determine if such thresholds will be exceeded in the short term. They found that although the average global temperature will not exceed 1.5°C over the next five years, there is a 38 percent chance it will temporarily exceed it on a monthly basis, and a 10 percent chance it will exceed it on an annual basis.