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A small number of “ultra-emitters” of methane from oil and gas production contribute as much as 12 percent of emissions of the greenhouse gas to the atmosphere every year — and now scientists know where many of these sources are.

Analyses of satellite images from 2019 and 2020 reveal that a majority of the 1,800 biggest methane sources come from six major oil- and gas-producing countries: Turkmenistan led the pack, followed by Russia, the United States, Iran, Kazakhstan and Algeria.

Plugging those leaks would not only be a boon to the planet, but also could save those countries billions in U.S. dollars, climate scientist Thomas Lauvaux of the University of Paris-Saclay and colleagues report in the Feb. 4 Science.

Ultra-emitters are sources that spurt at least 25 metric tons of methane per hour into the atmosphere. These occasional massive bursts make up only a fraction — but a sizable one — of the methane shunted into Earth’s atmosphere annually.

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Cleaning up such leaks would be a big first step in reducing overall emissions, says Euan Nisbet, a geochemist at Royal Holloway, University of London in Egham, who was not involved in the study. “If you see somebody badly injured in a road accident, you bandage up the bits that are bleeding hardest.”

Methane has about 80 times the atmosphere-warming potential of carbon dioxide, though it tends to have a much shorter lifetime in the atmosphere — 10 to 20 years or so, compared with hundreds of years. The greenhouse gas can seep into the atmosphere from both natural and human-made sources (SN: 2/19/20).

In oil and gas production, massive methane bursts might be the result of accidents or leaky pipelines or other facilities, Lauvaux says. But these leaks are often the result of routine maintenance practices, the team found. Rather than shut down for days to clear gas from pipelines, for example, managers might open valves on both ends of the line, releasing and burning off the gas quickly. That sort of practice stood out starkly in satellite images as “two giant plumes” along a pipeline track, Lauvaux says.

Stopping such practices and repairing leaky facilities are relatively easy, which is why such changes may be the low-hanging fruit when it comes to addressing greenhouse gas emissions. But identifying the particular sources of those huge methane emissions has been the challenge. Airborne studies can help pinpoint some large sources, such as landfills, dairy farms and oil and gas producers, but such flights are limited by being both regional and of short duration (SN: 11/14/19).

Satellites, such as the European Space Agency’s Tropospheric Monitoring Instrument, or TROPOMI, offer a much bigger window in both space and time. Scientists have previously used TROPOMI to estimate the overall leakiness of oil and gas production in Texas’s massive Permian Basin, finding that the region sends twice as much methane to the atmosphere as previously thought (SN: 4/22/20).

In the new study, the team didn’t include sources in the Permian Basin among the ultra-emitters; the large emissions from that region are the result of numerous tightly clustered but smaller emissions sources. Because TROPOMI doesn’t peer well through clouds, other regions around the globe, such as Canada and the equatorial tropics, also weren’t included.

But that doesn’t mean those regions are off the hook, Lauvaux says. “There’s just no data available.” On the heels of this broad-brush view from TROPOMI, Lauvaux and other scientists are now working to plug those data gaps using other satellites with better resolution and the ability to penetrate clouds.

Stopping all of these big leaks, which amount to an estimated 8 to 12 percent of total annual methane emissions, could save these countries billions of dollars, the researchers say. And the reduction in those emissions would be about as beneficial to the planet as cutting all emissions from Australia since 2005, or removing 20 million vehicles from the roads for a year.

Such a global map can also be helpful to countries in meeting their goals under the Global Methane Pledge launched in November at the United Nations’ annual climate summit, says Daniel Jacob, an atmospheric chemist at Harvard University who was not involved in the study (SN: 1/11/22).

Signatories to the pledge agreed to reduce global emissions of the gas by at least 30 percent relative to 2020 levels by 2030. These new findings, Jacob says, can help achieve that target because it “encourages action rather than despair.”  More

Extremes in rainfall — whether intense drought or flash floods — can catastrophically slow the global economy, researchers report in the Jan. 13 Nature. And those impacts are most felt by wealthy, industrialized nations, the researchers found.

A global analysis showed that episodes of intense drought led to the biggest shocks to economic productivity. But days with intense deluges — such as occurred in July 2021 in Europe — also produced strong shocks to the economic system (SN: 8/23/21). Most surprising, though, was that agricultural economies appeared to be relatively resilient against these types of shocks, says Maximilian Kotz, an environmental economist at the Potsdam Institute for Climate Impact Research in Germany. Instead, two other business sectors — manufacturing and services — were the most hard-hit.

As a result, the nations most affected by rainfall extremes weren’t those that tended to be poorer, with agriculture-dependent societies, but the wealthiest nations, whose economies are tied more heavily to manufacturing and services, such as banking, health care and entertainment.

It’s well established that rising temperatures can take a toll on economic productivity, for example by contributing to days lost at work or doctors’ visits (SN: 11/28/18). Extreme heat also has clear impacts on human behavior (SN: 8/18/21). But what effect climate change–caused shifts in rainfall might have on the global economy hasn’t been so straightforward.

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That’s in part because previous studies looking at a possible connection between rainfall and productivity have focused on changes in yearly precipitation, a timeframe that “is just too coarse to really describe what’s actually happening [in] the economy,” Kotz says. Such studies showed that more rain in a given year was basically beneficial, which makes sense in that having more water available is good for agriculture and other human activities, he adds. “But these findings were mainly focused on agriculturally dependent economies and poorer economies.”

In the new study, Kotz and his colleagues looked at three timescales — annual, monthly and daily rainfall — and examined what happened to economic output for time periods in which the rainfall deviated from average historical values. In particular, Kotz says, they introduced two new measures not considered in previous studies: the amount of rainy days that a region gets in a year and extreme daily rainfall. The team then examined these factors across 1,554 regions around the world — which included many subregions within 77 countries — from 1979 to 2019.

The disparity over which regions are hit hardest is “at odds with the conventional wisdom” — and with some previous studies — that agriculture is vulnerable to extreme rainfall, writes Xin-Zhong Liang, an atmospheric scientist at the University of Maryland in College Park, in a commentary in the same issue of Nature. Researchers may need to incorporate other factors in future assessments, such as growth stages of crops, land drainage or irrigation, in order to really understand how these extremes affect agriculture, Liang writes.

“That was definitely surprising for us as well,” Kotz says. Although the study doesn’t specifically try to answer why manufacturing and services were so affected, it makes intuitive sense, he says. Flooding, for example, can damage infrastructure and disrupt transportation, effects that can then propagate along supply chains. “It’s feasible that these things might be most important in manufacturing, where infrastructure is very important, or in the services sectors, where the human experience is very much dictated by these daily aspects of weather and rainfall.”

Including daily and monthly rainfall extremes in this type of analysis was “an important innovation” because it revealed new economic vulnerabilities, says Tamma Carleton, an environmental economist at the University of California, Santa Barbara, who was not involved in the new work. However, Carleton says, “the findings in the paper are not yet conclusive on who is most vulnerable and why, and instead raise many important questions for future research to unpack.”

Extreme rainfall events, including both drought and deluge, will occur more frequently as global temperatures rise, the United Nations’ Intergovernmental Panel on Climate Change noted in August (SN: 8/9/21). The study’s findings, Kotz says, offer yet another stark warning to the industrialized, wealthy world: Human-caused climate change will have “large economic consequences.” More

What’s in a number? The goals of the 2021 United Nations’ climate summit in Glasgow, Scotland, called for nations to keep a warming limit of 1.5 degrees Celsius “within reach.” But when it comes to communicating climate change to the public, some scientists worry that too much emphasis on a specific number is a poor strategy.

Focusing on one number obscures a more important point, they say: Even if nations don’t meet this goal to curb global climate change, any progress is better than none at all. Maybe it’s time to stop talking so much about one number.

On November 13, the United Nations’ 26th annual climate change meeting, or COP26, ended in a new climate deal, the Glasgow Climate Pact. In that pact, the 197 assembled nations reaffirmed a common “ideal” goal: limiting global warming to no more than 1.5 degrees C by 2100, relative to preindustrial times (SN: 12/17/18).

Holding temperature increases to 1.5 degrees C, researchers have found, would be a significant improvement over limiting warming to 2 degrees C, as agreed upon in the 2015 Paris Agreement (SN: 12/12/15). The more stringent limit would mean fewer global hazards, from extreme weather to the speed of sea level rise to habitat loss for species (SN: 12/17/18).

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The trouble is that current national pledges to reduce greenhouse gas emissions are nowhere near enough to meet either of those goals. Even accounting for the most recent national pledges to cut emissions, the average global temperature by 2100 is likely to be between 2.2 and 2.7 degrees C warmer than it was roughly 150 years ago (SN: 10/26/21).

And that glaring disparity is leading not just to fury and frustration for many, but also to despair and pervasive feelings of doom, says paleoclimatologist Jessica Tierney of the University of Arizona in Tucson.

“It’s something I’ve been thinking about for a while, but I think it was definitely made sort of more front and center with COP,” Tierney says. She describes one news story in the wake of the conference that “mentioned 1.5 degrees C, and then said this is the threshold over which scientists have told us that catastrophic climate change will occur.”

The article reveals a fundamental misunderstanding of what the agreed-upon limit really represents, Tierney explains. “A lot of my students, for example, are really worried about climate change, and they are really worried about passing some kind of boundary. People have this idea that if you pass that boundary, you sort of tip over a cliff.”

The climate system certainly has tipping points — thresholds past which, for example, an ice sheet begins to collapse and it’s not possible to stop or reverse the process. But, Tierney says, “we really should start communicating more about the continuum of climate change. Obviously, less warming is better.” However, “if we do blow by 1.5, we don’t need to panic. It’s okay if we can stop at 1.6 or 1.7.”

Tierney notes that climate communications expert Susan Hassol, director of the Colorado-based nonprofit Climate Communication, has likened the approach to missing an exit while driving on the highway. “If you miss the 1.5 exit, you just slow down and take the next one, or the next one,” Tierney says. “It’s still better than hitting the gas.”

Target numbers do have some uses, notes climate scientist Joeri Rogelj of Imperial College London. After decades of international climate negotiations and wrangling over targets and strategies, the world has now agreed that 1.5 degrees C of warming is a desirable target for many countries, says Rogelj, who was one of the lead authors on the Intergovernmental Panel on Climate Change’s 2018 special report on global warming.

A global temperature limit “is a good proxy for avoiding certain impacts,” he adds. “These numbers are basically how to say this.”

But Rogelj agrees that focusing too much on a particular number may be counterproductive, even misleading. “There is a lot of layered meaning under those numbers,” he says. “The true interests, the true goals of countries are not those numbers, but avoiding the impacts that underlie them.”

And framing goals as where we should be by the end of the century — such as staying below 1.5 degrees C by the year 2100 — can give too much leeway to stall on reducing emissions. For example, such framing implies the planet could blow past the temperature limit by mid-century and rely on still-unproven carbon dioxide removal strategies to bring warming back down in the next few decades, Rogelj and colleagues wrote in 2019 in Nature.

Banking on future technologies that have yet to be developed is worrisome, Rogelj notes. After all, some warming-related extreme events, such as heat waves, are more reversible than others, such as sea level rise (SN: 8/9/21). Heat wave incidence may decrease once carbon is removed from the atmosphere, but the seas will stay high.

Rogelj acknowledges that it’s a challenge to communicate the urgency of taking action to reduce emissions now without spinning off into climate catastrophe or cliff edge narratives. For his part, Rogelj says he’s trying to tackle this challenge by adding a hefty dose of reality in his scientific presentations, particularly those aimed at nonscientists.

He starts with pictures of forest fires and floods in Europe from 2021. “I say, ‘Look, this is today, 1.1 degrees warmer than preindustrial times,’” Rogelj explains. “‘Do you think this is safe? Today is not safe. And so, 1.5 won’t be safer than today; it will be worse than today. But it will be better than 1.6. And 1.6 won’t be the end of the world.’ And that kind of makes people think about it a bit differently.” More

Africa’s “Great Green Wall” initiative is a proposed 8,000-kilometer line of trees meant to hold back the Sahara from expanding southward. New climate simulations looking to both the region’s past and future suggest this greening could have a profound effect on the climate of northern Africa, and even beyond.

By 2030, the project aims to plant 100 million hectares of trees along the Sahel, the semiarid zone lining the desert’s southern edge. That completed tree line could as much as double rainfall within the Sahel and would also decrease average summer temperatures throughout much of northern Africa and into the Mediterranean, according to the simulations, presented December 14 during the American Geophysical Union’s fall meeting. But, the study found, temperatures in the hottest parts of the desert would become even hotter.

Previous studies have shown that a “green Sahara” is linked to changes in the intensity and location of the West African monsoon. That major wind system blows hot, dry air southwestward across northern Africa during the cooler months and brings slightly wetter conditions northeastward during the hotter months.

Such changes in the monsoon’s intensity as well as its northward or southward extent led to a green Sahara period that lasted from about 11,000 to 5,000 years ago, for example (SN: 1/18/17). Some of the strongest early evidence for that greener Sahara of the past came in the 1930s, when Hungarian explorer László Almásy — the basis for the protagonist of the 1996 movie The English Patient — discovered Neolithic cave and rock art in the Libyan Desert that depicted people swimming.

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Past changes in the West African monsoon are linked to cyclical variations in Earth’s orbit, which alters how much incoming solar radiation heats up the region. But orbital cycles don’t tell the whole story, says Francesco Pausata, a climate dynamicist at the Université du Québec à Montréal who ran the new simulations. Scientists now recognize that changes in plant cover and overall dustiness can dramatically intensify those monsoon shifts, he says.

More vegetation “helps create a local pool of moisture,” with more water cycling from soil to atmosphere, increasing humidity and therefore rainfall, says Deepak Chandan, a paleoclimatologist at the University of Toronto who was not involved in the work. Plants also make for a darker land surface compared with blinding desert sands, so that the ground absorbs more heat, Chandan says. What’s more, vegetation reduces how much dust is in the atmosphere. Dust particles can reflect sunlight back to space, so less dust means more solar radiation can reach the land. Add it all up, and these effects lead to more heat and more humidity over the land relative to the ocean, creating a larger difference in atmospheric pressure. And that means stronger, more intense monsoon winds will blow.

The idea for Africa’s Great Green Wall came in the 1970s and ’80s, when the once-fertile Sahel began to turn barren and dry as a result of changing climate and land use. Planting a protective wall of vegetation to hold back an expanding desert is a long-standing scheme. In the 1930s, President Franklin Roosevelt mobilized the U.S. Forest Service and the Works Progress Administration to plant walls of trees from the Great Plains to Texas to slow the growth of the Dust Bowl. Since the 1970s, China has engaged in its own massive desert vegetation project — also nicknamed the Great Green Wall — in an attempt to halt the southward march of sand dunes from the Gobi Desert (SN: 7/9/21).

Led by the African Union, Africa’s Great Green Wall project launched in 2007 and is now roughly 15 percent complete. Proponents hope the completed tree line, which will extend from Senegal to Djibouti, will not only hold back the desert from expanding southward, but also bring improved food security and millions of jobs to the region.

What effect the finished greening might ultimately have on the local, regional and global climate has been little studied — and it needs to be, Pausata says. The initiative is, essentially, a geoengineering project, he says, and when people want to do any type of geoengineering, they should study these possible impacts.

To investigate those possible impacts, Pausata created high-resolution computer simulations of future global warming, both with and without a simulated wall of plants along the Sahel. Against the backdrop of global warming, the Great Green Wall would decrease average summertime temperatures in most of the Sahel by as much as 1.5 degrees Celsius.

But the Sahel’s hottest areas would get even hotter, with average temperatures increasing by as much as 1.5 degrees C. The greening would also increase rainfall across the entire region, even doubling it in some places, the research suggests.

These results are preliminary, Pausata says, and the data presented at the meeting were only for a high-emissions future warming scenario called RCP8.5 that may not end up matching reality (SN: 1/7/20). Simulations for moderate- and lower-emissions scenarios are ongoing.

The effects of greening the Sahara might extend far beyond the region, the simulations suggest. A stronger West African monsoon could shift larger atmospheric circulation patterns westward, influencing other climate patterns such as the El Niño Southern Oscillation and altering the tracks of tropical cyclones.

Chandan agrees that it’s important to understand just what impact such large-scale planting might have and notes that improvements in understanding what led to past changes in the Sahara are key to simulating its future. That the Great Green Wall’s impact could be far-ranging also makes sense, he says: “The climate system is full of interactions.” More