Center for Climate Sciences

The Arctic region is heating up twice as fast as the global average. Despite relatively few plant per area compared to the temperate and tropic regions, Arctic regions are key stores of soil organic carbon (SOC) which play a major role in the greenhouse gas balance of high-latitude ecosystems. Cold and sometimes moist environment conditions slow down the dead plant matter decomposition. This process emits the two most powerful greenhouse gases, methane (CH₄) and carbon dioxide (CO₂). While CH₄ emission accounts for a smaller component of the C balance, the climatic impact of CH₄ outweighs CO₂ (28-34 times larger Global Warming Potential on a 100-year scale), highlighting the need to jointly resolve the climatic sensitivities of CO₂ and CH₄.

Here we use a terrestrial biosphere model and field observations to understand what drives CO₂ and CH₄ exchanges in Alaska. Based on the combined CO₂ and CH₄ flux responses to climate variables, we find that 1970-present climate trends will induce positive C-climate feedback at all tundra sites (net warming effect), and negative C-climate feedback at the boreal and shrub fen sites (net cooling effect). The positive C-climate feedback at the tundra sites is predominantly driven by increased CH₄ emissions while the negative C-climate feedback at the boreal site is predominantly driven by increased CO₂ uptake (80% from slowed decomposition, and 20% from increased photosynthesis). This study demonstrates the need to jointly consider CO₂ and CH₄ biogeochemical processes – and their associated climatic sensitivities – in order to resolve the sign and magnitude of high-latitude ecosystem C-climate feedback in the coming decades.

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Heatwaves in California occur in both dry and humid forms, but recent studies indicate a shift towards more humid events. This research focuses on two contrasting heatwaves that affected southern California in the summer of 2020, providing an excellent opportunity to understand the impacts of humid versus dry heatwaves on the urban environment, specifically in the greater Los Angeles metropolitan region (as shown in figure 1). The results reveal that, despite the September heatwave having higher air temperatures, the humid heat stress – quantified using wet bulb temperature linked to the risk of heat stroke – was greater in August. While dry and humid heat display different spatial patterns, three distinct spatial clusters emerge based on non-heatwave local climates. Both types of heatwaves reduced the gradient of heat stress within the city, with valley areas experiencing the most significant increase in heat stress. Notably, valley regions such as San Bernardino and Riverside faced the most severe impacts, with up to a 6±0.5℃ additional heat stress during heatwave nights.

While Southern California is no stranger to extreme heat, these findings highlight the importance of including moist heat in extreme heat warning frameworks and considering the diverse impacts of heatwaves at a fine scale within urban areas. Such insights play a crucial role in designing policies that facilitate fair and effective mitigation strategies for extreme heat, ensuring equitable protection for all communities.

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In the quest to better understand Earth's ecosystems, scientists at Jet Propulsion Laboratory, California Institute of Technology and Oak Ridge National Laboratory, leveraging remote sensing data and Earth system modeling, have made significant strides in uncovering the global carbon costs associated with plant nutrient acquisition. Plants rely on nutrients in the soil to grow, including Nitrogen (for leaf growth) and Phosphorus (for root development and growing seeds, flowers, and fruit). However, declining levels of these nutrients are detrimental to plant health. This study used cutting-edge models to understand global plant nitrogen and phosphorus uptake. The results revealed that both nutrients co-limit 80% of the global land area, with plants investing a substantial amount of energy to acquire these nutrients from multiple uptake pathways, including symbiotic relationships with fungi - mycorrhiza.

The study's findings have significant implications for our understanding of land productivity worldwide and climate change predictions. By considering the carbon costs of nutrient acquisition, the model and observations agreement increased, reducing uncertainty in predictions. The use of remote sensing data in this study has enabled a more comprehensive and accurate representation of plant nutrient acquisition in Earth system models, paving the way for improved modeling and better insights into the global carbon cycle. This research highlights the importance of leveraging remote sensing techniques to gain valuable insights into complex Earth system processes and improve our understanding of global biogeochemical cycles.

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As concerns about climate change continue to mount, a recent study conducted by a team of scientists at Jet Propulsion Laboratory and California Institute of Technology has shed light on the effects of climate change on the Arctic-Boreal carbon balance. In recent history, some of the excess carbon dioxide we produce is taken up by forests (called a “carbon sink”), but there is concern that this benefit may not continue as the climate changes. This study used two groups of Earth system models to predict the future of vegetation for the North American Arctic-Boreal region.

Both model group ensembles suggested a tipping point in the Net Biome Production (NBP) curve, indicating that the Arctic-Boreal ecosystems may become less productive by 2050-2080 and will stop absorbing excess carbon dioxide in the next century. This information is significant for policymakers as it highlights the urgent need for climate change mitigation and adaptation strategies to address the potential shift in the carbon balance of this vulnerable region. Further research and action are required to better understand and mitigate the impacts of climate change in the Arctic-Boreal region and protect this critical carbon sink.

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