Research & Developments is a blog for brief updates that provide context for the flurry of news that impacts science and scientists today.

After more than half a century of Earth Days, one planetary challenge—climate change—threatens our planet more than ever.

In 1970, the year Sen. Gaylord Nelson (D-Wisc.) organized the first Earth Day events, the annual average concentration of carbon dioxide in the atmosphere was 326 parts per million. In 2025, it was 31% higher, at 427 parts per million. 

Changes in average annual temperatures in U.S. cities and states show the powerful effects of this increase in heat-trapping carbon dioxide. A new analysis, published today by climate research and communications nonprofit Climate Central, found that since 1970, all 50 states and 99% of major U.S. cities have warmed, with an average city-level increase of 1.6°C (2.9°F).

“It may sound small, but it’s reshaping daily life,” Shel Winkley, a meteorologist at Climate Central, said in a video released alongside the report. 

On average, the 49 U.S. states analyzed in the report have warmed by 1.7°C (3.0°F) since 1970. The six states that have warmed the fastest since the first Earth Day are Alaska with a 2.4°C (4.4°F) increase, New Jersey and New Mexico with a 2.1°C (3.7°F) increase, and Delaware, Massachusetts, and Vermont with a 2°C (3.6°F). Trends for Hawaii, which were analyzed separately and not included in the national average, also showed statewide warming.

In 2025, the United States was on average 1.4°C (2.6°F) warmer than the 20^th century average. The Paris Agreement, a legally binding global treaty, sets a goal to limit warming to 1.5°C (2.7°F) above preindustrial levels, though some scientists expect that the world has already entered the period of time during which this limit will be breached.

Warming trends in the United States are most pronounced in the Southwest, where cities have warmed an average of 1.9°C (3.5°F) since 1970. And in some cases, cities are warming much faster than whole states. Three of the five cities that have warmed the fastest since 1970 are in the Southwest: Reno, Nev., with an increase of 4.4°C (7.9°F), Las Vegas, with an increase of 3.3°C (6.0°F), and El Paso, Texas, with an increase of 3.3°C (5.9°F). 

The effects are evident at the national, state, and local levels. Temperatures have warmed in 240 of the 242 cities analyzed by Climate Central. Harrisonburg, VA and Monterey, CA were the only two cities analyzed that have not warmed since 1970.

The report highlights some good Earth Day news, however, and points out that solar and wind power generation is at an all-time high in the United States, accounting for 19% of the electricity generated in the country in 2025 despite those industries facing recent headwinds from the federal administration. 

“Every fraction of a degree [of warming] that we prevent does matter, for our health, for our communities, and for the world that we’re passing on to the next generations,” Winkley said. 

—Grace van Deelen (@gvd.bsky.social), Staff Writer

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Text © 2026. AGU. CC BY-NC-ND 3.0
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Planting more trees will decelerate climate change only if those trees are placed in optimal locations—primarily the tropics and subtropics—suggests new research published in Communications Earth and Environment. However, planting trees in locations like Alaska, Siberia, and large parts of the United States could actually lead to warming, said lead author and doctoral student at ETH Zurich Nora Fahrenbach.

Much of the current thinking in nature-based solutions, Fahrenbach said, is based on the idea that “more is better.”

As in, “we’ll plant a trillion trees, or we’ll plant more than a trillion trees, and we are going to get more cooling, right?” Fahrenbach said. “That’s something we show is just not the case.”

Fahrenbach researches reforestation potentials, or global maps that identify areas where trees could be planted to mitigate climate change. In this work, she and her colleagues compared three prominent reforestation potentials to determine the effect of tree placement on local and global temperatures.

One scenario involved reforesting about 926 million hectares focused mostly on the tropics and resulted in about 0.25°C of cooling by 2100. Another called for reforesting 894 million hectares, including large areas in northern temperate and polar latitudes, and resulted in 0.13°C of cooling by 2100.

The third scenario involved planting forests strategically over only 440 million hectares of mostly tropical and subtropical land (less than half of the area covered in the other scenarios) but also resulted in 0.13°C of cooling. Geography, the findings suggest, may matter more than quantity when it comes to the cooling benefits of reforestation efforts.

Let’s Get (Biogeo)physical

The researchers modeled all three scenarios using the same parameters: Trees were planted from 2015 to 2070 and then remained steady in their population until 2100.

All three models identified reforestation opportunities in regions such as the eastern United States, Amazonia, the Congo rainforest, and eastern China, as well as regions for which reforestation would not be as impactful, such as polar regions in the Northern Hemisphere. The researchers also found significant temperature changes across the Atlantic and Indian oceans as a result of atmospheric changes induced by reforestation, demonstrating an interconnected reality: Planting trees in one area doesn’t just change the local temperature but has effects across the world.

These local and nonlocal effects can be explained by a combination of biogeochemical and biogeophysical effects.

A biogeochemical effect relates to the movement of chemicals or chemical elements, such as trees absorbing carbon from the atmosphere.

A biogeophysical effect relates to the physical results of changing the land’s surface: Placing a tree in a snowy region, for instance, decreases the land’s albedo, meaning it causes the land surface to become darker and absorb more light, leading to more local heat. This rise in surface temperature also raises air temperature, creating cascading effects on wind patterns and oceanic currents.

Considering both processes together is essential for understanding whether a net cooling or net heating effect exists, but most policies focus only on biogeochemical effects, seeing trees solely for their ability to absorb carbon from the atmosphere, Fahrenbach said. They include prominent international policies such as the Paris Agreement and the United Nations’ Framework for REDD+.

“Really, we would also need to consider the biogeophysical effects,” Fahrenbach said. “That’s harder to do, right, considering those nonlocal effects, because just imagine, some country is going to plant a lot of trees, and that’s going to lead to warming somewhere else.”

A Call to Policymakers

Emilio Vilanova, a forest ecologist at the climate action nonprofit Verra, wrote by email, “The most important message for me is that this study emphasizes something that is often not well addressed in reforestation projects: Reforestation is not just about planting trees—it’s about designing where new forests go to maximize benefits and avoid unintended consequences.”

Vilanova also said the study puts the potential for reforestation efforts to address climate change in perspective. “Even very large reforestation efforts would only reduce global temperatures by about 0.13–0.25°C by the end of the century,” he said. “While meaningful, this finding also reinforces that reforestation is a helpful tool, not a stand-alone solution to climate change.”

Though the limited potential for change is sobering, the authors and Vilanova pointed out that this change does matter and that it matters how we think of our approach. They advocate for policies that adopt reforestation strategies based on location and that acknowledge both the local and nonlocal effects of reforestation.

“We really need to make sure that where we plant first, it has benefits locally, it has benefits globally,” Fahrenbach said.

—Andrew Meissen (@AndrewMeissen), Science Writer

22 April 2026: This article was updated to correct Nora Fahrenbach’s position at ETH Zurich.

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Citation: Meissen, A. (2026), Location, location, location: The “where” of reforestation may matter more than the extent, Eos, 107, https://doi.org/10.1029/2026EO260125. Published on 22 April 2026.

Text © 2026. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Editors’ Highlights are summaries of recent papers by AGU’s journal editors.

Source: AGU Advances

The evolution of rivers that split into multiple channels is a scientific challenge in terms of modeling and prediction. On the other hand, these rivers are widespread and play a key role for ecosystems’ life, groundwater recharge, and therefore, water security. They are also extremely sensitive to hydroclimatic changes, leading to shifts in precipitation, erosion and sediment transport.

Zhao et al. [2026] investigate the drivers of river evolution for 97 multithread river reaches worldwide, spanning diverse climates and morphologies. The study reveals the key role of intermittency for river evolution. In particular, higher flow intermittency could lead to more even flow partitioning among threads, therefore impacting hydrology and ecosystems. With flow variability increasing after climate change, rivers are likely to increase their thread count, thus impacting livelihoods and ecosystems.

Citation: Zhao, F., Ganti, V., Chadwick, A., Greenberg, E., McLeod, J., Liu, Y., et al. (2026). Global hydroclimatic controls on multithread River dynamics. AGU Advances, 7, e2025AV002166. https://doi.org/10.1029/2025AV002166

—Alberto Montanari, Editor-in-Chief, AGU Advances

Text © 2026. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.