The past year was pivotal in climate research, even though the COVID-19 pandemic, Black Lives Matter demonstrations, and the U.S. presidential election dominated the news cycle. As the pandemic limited field and laboratory work, many researchers pivoted to spend more time polishing and submitting manuscripts.
The Proceedings of the National Academy of Sciences (PNAS) had an increase of about 20% in submissions last year, said May Berenbaum, editor-in-chief.
“Although to date our most highly cited papers were overwhelmingly COVID-related, climate change publications are still attracting tremendous attention, evidence that even the existential threat posed by the pandemic has not shifted attention away entirely from climate change,” Berenbaum says.
While some researchers were able to submit more papers than usual, the pandemic did not affect everyone equally. Many female scientists and those with young children found their research disrupted and negatively impacted by the pandemic, according to a July study in Nature Human Behaviour. Publishing and research disparities have been widely reported, with women shouldering a disproportionate share of childcare and household duties, leaving less time to devote to research and publishing.
The editors of four major journals – Science, PNAS, Nature and Geophysical Research Letters – shared their thoughts on 2020’s most intriguing research. The studies have implications for a wide range of activities, from food and water supplies to urban planning, preserving polar ice and looking more closely at how mountains and mountain ranges act as “water towers” that supply fresh water to vast regions of Earth.
Jesse Smith, senior editor at Science, points to four pivotal 2020 climate change studies focusing on a few different topics, including megadrought, marine heatwaves, food systems emissions, and tropical forests.
One of Smith’s selections, “Large contribution from anthropogenic warming to an emerging North American megadrought” by Williams et al., delves into drought patterns in southwestern North America (SWNA), finding conditions between 2000-2018 to be the “second driest 19-year period since 800 CE.” The study attributed 46% of the drought severity during that period to anthropogenic impacts. The study notes these trends are “pushing an otherwise moderate drought onto a trajectory comparable to the worst SWAN megadroughts since 800 CE.” This is alarming given the region’s growing need for water, including for agriculture and energy production.
“Drought is one of those cardinal issues involved in figuring out what’s happening with climate change, and this paper was technically so well done and offered such a compelling argument that the warming we’re causing from human activity is impacting, in a really tangible way, the hydrological cycle here in, of course, the American West, but similar arguments can be made for other places in the world too,” Smith says.
Rising ocean temperatures are also a growing problem. Marine heatwaves can harm ecosystems, human food systems, and more. In “High-impact marine heatwaves attributable to human-induced global warming” by Laufkötter et al., the authors examined these heat waves.
“This paper shows that these marine heatwaves have increased in frequency, duration and intensity by a factor between 3 and 10 over the past 20 years,” Smith says. “These marine events, like their terrestrial counterparts, can be extremely harmful to species and food webs and thus are notable for their impacts on existing ecosystems.”
Smith also points to an article about feeding the planet. In “Global food system emissions could preclude achieving the 1.5° and 2°C climate change targets” by Clark et al., the authors note current food production systems may prevent attainment of Paris Agreement climate goals. It noted, “even if fossil fuel emissions were immediately halted, current trends in global food systems would prevent the achievement of the 1.5°C target and, by the end of the century, threaten achievement of the 2°C target.” They note “rapid and ambitious changes to food systems” would be necessary – in addition to changes in other sectors – to meet the 1.5°C target.
“Feeding the world is an issue of absolute paramount importance … We can’t stop agriculture, we can’t stop feeding people – we need to feed more people,” Smith says. “There’s a lot of food insecurity in the world, so how we go about growing food and producing food, how agriculture can be modified to meet everybody’s needs, plus not harming climate, that’s a question that nobody can deny is important.” The study mentions a number of potential strategies to reduce the greenhouse gas emissions from food production, such as eating a plant-rich diet, using strategies to produce higher crop yields and reduce emissions during production, and reducing food waste.
Smith points out another study, “Long-term thermal sensitivity of Earth’s tropical forests,” by Sullivan et al., that analyzes 590 plots around the tropics. They emphasize the importance of protecting these forests to stabilize climate and adapt to climate change.
“The Amazon has been called ‘the lungs of the Earth’ and it really is,” Smith says. “The Amazon in particular is one of the major parts of how the terrestrial biosphere affects climate and the amount of CO2 in the atmosphere. The carbon cycle is heavily dependent on the dynamics of tropical forest systems … We’ve known for a long time how important tropical forests are for climate and carbon cycle. This paper is notable because it’s such a clear demonstration of exactly how temperatures – which are warming, of course, at an incredible rate right now – are affecting the carbon stocks of these tropical forests. It’s one of the cardinal issues in climate, ecosystems, and carbon cycling.”
Michael White, senior editor at Nature, selected articles focusing on European flooding, the melting Antarctic Ice Sheet and factors that affect the ability of mountain ranges to act as natural “water towers” storing ice at high elevations and ultimately refreshing rivers and water tables at lower altitudes.
In “Importance and vulnerability of the world’s water towers” by Immerzeel et al., the authors focus on mountains they call “water towers of the world” because they hold so much vital water. The authors develop a “water tower index” ranking them according to the water they supply and how people and ecosystems rely on them, noting 22% of the world’s population relies on water tower units for their water.
He cites how the paper covers a multitude of topics, saying, “In many cases, you find that you have a bunch of physical scientists that are trying to quantify the degree to which water towers or glacial systems are supplying water,” White says. “But it’s much rarer that they will actually try to engage with the systemic vulnerability of these areas or, much less, with the political systems.”
White also points to Blöschl et al.’s article “Current European flood-rich period exceptional compared with past 500 years” which examines historic European flood records. The authors found the “past three decades were among the most flood-rich periods in Europe in the past 500 years.” While in the past, flood-rich periods typically occurred during colder periods, more recently flooding has occurred during warmer periods. White found the study’s collaborative aspects particularly intriguing.
“What’s so cool about this paper is you have a whole bunch of physical scientists working with a whole bunch of historians, and they’re really doing the best job they can to go back and look at the written records of flooding in Europe, which is the best documented place we have in the world for this kind of stuff, to do this reconstruction,” White says.
White also discussed Garbe et al.’s paper “The hysteresis of the Antarctic Ice Sheet,” exploring the potential fate of the Antarctic Ice Sheet – which contains over half the world’s freshwater and will impact global sea level rise upon melting. The authors found, “the Antarctic Ice Sheet exhibits a multitude of temperature thresholds beyond which ice loss is irreversible.” They found in order to regrow ice, temperatures would have to drop below present-day levels and, in some cases, below pre-industrial levels.
“People have been talking a lot about the idea of a climate overshoot, so there’s been hope or discussion that even if in the near term we can’t keep the climate below 1.5°C of overall warming, maybe we can kind of allow it to exceed that for a while up to 2-2.5°C, and then through aggressive mitigation and carbon capture and storage and techniques … we can then pull the system back down to a lower state,” White says. “But what they’re showing here is that this doesn’t work for the ice sheet. … And the level of cooling that’s required to get down to the previous state is much larger than the warming that’s required to do the melting itself. I found it a fairly alarming conclusion and one that really highlights the need to take mitigation more seriously in the near term and not just rely on the idea of overshoot and negative emissions.”
Proceedings of the National Academy of Sciences (PNAS)
Editor-in-chief May Berenbaum points to three standout 2020 articles she says have had a significant impact on scientific literature and were also widely shared on social media and outside the scientific community. The first one involves social tipping points, described as points in a social system where small changes can trigger more rapid changes “driven by self-reinforcing positive-feedback mechanisms” that can result in substantial changes to the social system and help the world meet the Paris Agreement goals.
Berenbaum mentions that in “Social tipping dynamics for stabilizing Earth’s climate by 2050,” Otto, et al. note that “after three decades of relatively ineffective responses to calls for change, implementation of social interventions could be critical for bringing about global transformation to carbon neutrality by 2050.”
The study examines interventions such as removing fossil fuel subsidies, creating carbon neutral cities, divesting from fossil fuels, increasing climate literacy, and more. The article was followed by a letter to the editor, and then a reply from the study’s authors. “The main thrust of both the letter and the reply is that rapid change is unlikely to result by simply relying on governmental efforts, but rather will require a seismic sociocultural shift,” Berenbaum notes.
Berenbaum’s also singled-out “Future of the human climate niche” by Xu, et al. Many humans – along with the crops and livestock they depend on – have lived within a fairly narrow temperature range for thousands of years, with a mean annual temperature around 13°C. If climate change continues unabated, the geographical area with this ideal range will shift dramatically over the next five decades. The authors predict up to a third of the world’s population will be faced with Sahara desert-like temperatures, with a mean annual temperature over 29°C. People will either have to migrate or do their best to adapt.
“Dramatic shifts in this distribution may leave millions of people outside the narrow boundaries and thereby exposed to hitherto unprecedented climate stresses absent redistributions through migrations, with its attendant challenges,” Berenbaum says.
Berenbaum points also to Ceballos et al.’s article “Vertebrates on the brink as indicators of biological annihilation and the sixth mass extinction.” It analyzes 29,400 terrestrial vertebrate species, finding 515 are “on the brink of extinction,” and noting “the human-caused sixth mass extinction is likely accelerating.”
“These authors mined existing literature to compare key features of terrestrial vertebrates assessed as threatened by extinction” with features of species judged more secure in order “to identify the common characteristics and dynamics of declines to the brink and ultimately extinction,” Berenbaum says. The study also goes on to note the ripple effects each extinction may have by imperiling biodiversity and harming ecological interactions, noting “extinction breeds extinctions.”
Geophysical Research Letters
Alessandra Giannini, editor at Geophysical Research Letters, says the standout articles of 2020 for her include two focusing on climate change in the tropics and a third focused on the importance of theory in climate change research.
Hsiao et al.’s “Investigating Recent Changes in MJO Precipitation and Circulation in Multiple Reanalyses” examined the Madden-Julian Oscillation (MJO) which Giannini explains is “the most significant coherent manifestation of tropical climate at sub-seasonal timescale.” The study was alarming because it found future predicted changes involving wind and precipitation are already occurring. “This article shows that changes in features of the MJO that are projected in models to occur in response to warming at the end of the 21st century, have, in fact already occurred.” Giannini says.
In Song et al.’s “Contrasting phase changes of precipitation annual cycle between land and ocean under global warming,” researchers analyzed the timing of seasonal monsoon rainfall, which 40% of the world relies on for water. They found that with a warmer world, seasonal rainfall delays may occur over land, which could have serious implications for residents.
“The seasons in most tropical or monsoon regions are really dictated [by] ‘is it the rainy season or is it the dry season?'” Giannini says. “Even minor changes in the timing of these seasons can have significant consequences.”
For a third selection, Giannini pointed to a piece by Kerry Emanuel of MIT on “The Relevance of Theory for Contemporary Research in Atmospheres, Oceans, and Climate.” In this paper, Emanuel “argues that simulation without understanding imperils scientific progress and, paradoxically, may impede the development of better models.”
Giannini says the science of climate has evolved drastically over the past 50 years: “There is so much more we still need to understand,” she says, adding that she believes Emanuel “was asking for a better balance between these three aspects – the theory, the observations, and the model.” She said she believes this approach will contribute to improved understanding of the system as a whole.