Tropical forests face ‘substantial carbon loss’ as humid areas contract
The reduction of humid regions in a warming climate could cause “substantial carbon loss” across the tropics by the end of the century, a new study finds.
The research, published in Nature Climate Change, assesses the potential changes in the distribution of wet and dry regions in tropical ecosystems by 2100 – under two different emissions scenarios – and the subsequent carbon loss that may occur due to these shifts.
The study projects a decrease in the extent of humid regions of tropical ecosystems and an expansion of areas with intense dry periods over the next several decades.
Come rain or come shine: How is climate change impacting precipitation along Kachemak Bay?
Last year in Homer, a warm, dry spring gave way to a very damp, gray summer. For Paul Castellani of Will Grow Farm, handling whatever the weather brings is business as usual. He and his wife Jen have been growing vegetables at their property near Anchor Point for two decades.
“It wasn’t an extraordinary summer,” Castellani said, “except for the way that the two types of conditions were so separated.”
The early dry spell meant the Castellanis had to pay close attention to irrigating their carrot beds to make sure the seeds stayed moist, although cool, clear nights offered their crops some much-needed morning dew. But by the end of the season, getting their storage onions to cure with the cloudy, rainy conditions was a challenge.
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Drought in the Western U.S. has plunged the largest reservoir in the country into alarming shortage conditions that have rippling impacts for the region. Lake Mead, formed by the construction of the Hoover Dam on the Colorado River, delivers water and hydroelectric power to 25 million residents in the Southwest. But its viability has been pushed to the brink by intensifying drought, exacerbated by climate change, triggering emergency measures to conserve water in the basin.
The region has been in a “megadrought” since 2000, but recently, Lake Mead’s water levels have been breaking ever lower lows, unearthing old shipwrecks and other long-forgotten debris and leaving a “bathtub ring” around the reservoir’s edges. The drought signals a larger trend of dwindling snowfall and longer summers brought on by the growing climate crisis.
New water scarcity measures enacted
Water usage on the Colorado River operates on a tier system. When water levels in a reservoir drop below a certain point, usage by neighboring states is restricted. Lake Mead hit Tier 1 in August 2021 after the elevation of the reservoir dipped below 1,075 feet, leading to a reduction in water supplies that largely impacted agricultural users across counties.
This was the first time a shortage condition has been implemented on Lake Mead. The Tier 2 decision was announced in August of 2022—stating that the water level would fall below 1,050 by the end of the year, triggering a more intense shortage.
This emergency declaration for Lake Mead is part of a plan to increase the water levels in Lake Powell— an upstream reservoir and the second largest in the United States behind Mead. Dealing with shortages in the Colorado River Basin has required officials to weigh the needs of one region over another. The Bureau of Reclamation has indicated that at present, keeping water levels up in Lake Powell supersedes the requirements of Lake Mead. The generators at Powell have a total capacity of 1,320 megawatts and the reservoir is considered a ‘bank account’ for the region to draw on in times of drought—which are anticipated to worsen with climate change.
According to the US Drought Monitor, extreme droughts were rare in the historical climate—a 5.5% likelihood. In 2022 however, nearly all of the watersheds in the Colorado River experienced extreme drought. In a world warmed by 2 degrees C, the likelihood of 12 or more months of extreme drought in the Colorado River Basin becomes as high as 40%.
Meeting water needs in dry times
But Lake Mead also serves a massive population in the lower basin, and filling demand for water even during shortages means some major cities have to turn to reservoirs on other river systems. Arizona, suffering some of the steepest cuts in their allotment of Colorado River water (21%) , will draw from the Salt and Verde rivers. Other strategies include pumping groundwater and implementing more aggressive conservation and re-use strategies, which have so-far helped to spare Las Vegas from the worst effects of the shortage.
The Southern Nevada Water Authority also began using its low lake level intake in 2022, which allows the state to draw water even when the elevation of the lake falls below “dead pool” status— the point at which downstream water releases are no longer possible. But this is only a temporary solution, as the water in the reservoir keeps falling.
The next significant threshold for Lake Mead would be a drop to Tier 3 (1,025 feet) which some experts say could come as soon as 2024. At 950 feet, the reservoir would be considered an “inactive pool”, meaning the dam’s generators can no longer run. Energy shortages could kick off a vicious cycle, requiring backfilling with fossil fuels that would exacerbate the climate crisis and warming-driven drought conditions.
Reversing the drought in the Colorado River Basin will ultimately depend on snowfall in the Rocky Mountains, which will ultimately depend on getting the climate crisis under control. Experts estimate there would have to be several consecutive heavy snow years in the mountains to make back the current deficits further downriver. 2023 is currently experiencing above average snowpack, but if temperatures keep rising, that will be a less likely annual occurrence. Water rights and resource usage will have to adapt rapidly to support residents as reservoir levels continue to drop, but pulling out of emergency scarcity measures for good will require curbing the greater impacts of global climate change.
Extreme cold snaps: Why temperatures still plummet to dangerous levels even as the planet warms
Even as the world smashes through one all-time heat record after another and speeds towards critical warming thresholds, brutal waves of deadly cold can still arrive in bomb cyclones that bring icy weather and deep snow – and add fuel for those who deny the climate crisis is real or significant.
But some scientists say that climate change – and more specifically rapid warming in the Arctic – may actually be increasing the likelihood that frigid, polar air can dive south.
Global climate change
Mark Oppenheim leads a discussion on climate change and the role of humanity, with special guests: Dr. Nathaniel Keohane, President of the Center for Climate and Energy Solutions; Dr. R. Max Holmes, President and CEO of Woodwell Climate Research Center; & Erich Pica, President of Friends of the Earth & Friends of the Earth Action.
It’s in the rules to play dirty in this new soil-themed board game
Scientists designed the free-to-play game ‘Dirty Matters’ to help us appreciate this overlooked substance.
Scientists who research soil by day and play board games at night designed a new activity they hope will make their jobs easier to explain to their family, and even more importantly, the world.
Tanvi Taparia, a postdoctoral researcher at the University of Copenhagen, studies how soil biology affects plant health and growth, which in turn affects how much food farmers can produce. She helped design a board game, wittily named Dirty Matters, that illustrates soil’s role in achieving food security, clean water, and carbon storage, three of United Nations sustainable development goals. The game is free and available to download for the public online. Interested players can print out the board game, cards, and characters.
What’s New?
Recent research has quantified the cumulative impact of dams on Brazil’s native savanna ecosystem, the Cerrado. The study created an index of the direct and indirect impacts of constructing hydroelectric facilities on both the rivers being dammed and the surrounding ecosystem.
While often offered as a cleaner alternative to fossil fuels, dams can have severe environmental impacts ranging from deforestation to obstruction of fish migrations, water pollution, and even direct greenhouse gas emissions resulting from inundation of the surrounding area. This study assessed these effects cumulatively, weighting them more heavily if multiple dams were present in a single watershed.
“For freshwater systems, there’s not the equivalent of a deforestation rate. We don’t have an easy metric of ecosystem damage. So this study was one way of building a method for assessing the unintended consequences of installing a dam in a Cerrado watershed,” says Woodwell Water program director Dr. Marcia Macedo, who collaborated on the paper.
The study puts forward a new Dam Saturation Index (DSI) for the region to approximate the environmental impacts of existing dams. High-saturation watersheds were concentrated in the central and western portions of the biome, and most planned dams are located in sensitive areas of native vegetation with little protection.
Understanding hydropower in Brazil
Hydropower is big in Brazil—66% of the country gets some or all of their energy from it. Harnessing the power of a river is often the easiest means of electricity production in rural and remote areas. However, large hydroelectric plants are more often used as a means of infrastructural support for extractive industries like mining, rather than to expand access to electricity for rural citizens. Conflicts have already arisen between communities and hydroelectric plants.
Conflict over water usage in the Cerrado is expected to increase as the region continues to get hotter and dryer due to human-caused climate change. Land use change in the biome has accelerated the impacts of climate change, removing the cooling and moisture-retaining effects of natural vegetation.
“There are a lot of dams already, and many more planned, and it’s only going to get more contentious as climate change continues,” Dr. Macedo says. “In the northern and eastern part of the Cerrado, it’s already quite dry. We’re already seeing conflict over water and these reservoirs could just make that worse as upstream locations are able to withhold water from those downstream.”
What this means for the Cerrado
The Cerrado has historically not garnered as much attention, or as many demands for its protection, as the neighboring Amazon rainforest. Less than 10% of the Cerrado is considered protected, and many of those protections are biased toward terrestrial habitats and species. Lack of research into the full impact of hydropower on the watersheds of the Cerrado has left the region vulnerable to unchecked development. Some dams have even been built in areas otherwise strictly protected. Dr. Macedo hopes this study will encourage a different attitude towards freshwater resources.
“There is a question of how we can innovate thinking about protecting freshwater systems, especially under climate change. They’re so important, and there are so many resources—fisheries and clean water and more—that come from these systems,” Dr. Macedo says.
This study focused on large hydroelectric dams, but Dr. Macedo notes that there are many more small dams, built to serve individual farms, that also impact the flow of headwater streams. Ongoing research is focused on understanding the cumulative impacts of dams of all sizes on tropical watersheds.
This study focused on large hydroelectric dams, but Dr. Macedo notes that there are many more small dams, built to serve individual farms, that also impact the flow of headwater streams. Ongoing research is focused on understanding the cumulative impacts of dams of all sizes on tropical watersheds.