Research – At a Glance

Stephen Pacala: Pacala’s lab focused on three areas in 2019: 1) They continued their work on the terrestrial biosphere and carbon cycle, and on the role of land use change in carbon mitigation. They completed a series of studies that improve the effects of drought on the carbon cycle in climate models, particularly in the tropics. Also, Pacala spent a large amount of his time completing the National Academy of Sciences report on negative emissions technologies. He chaired the effort and co-wrote the chapters on negative emissions from land use change. 2) They continued their work on the possibility that tropical forests may be spontaneously switching to vine-dominance, which would cause them to lose 95% of their carbon to the atmosphere. This is a possible new tipping point. They expect to have an answer by the 2020 Carbon Mitigation Initiative (CMI) annual meeting. 3) They started a large project on net-zero-emitting infrastructure for the United States. Although organized initially by the CMI, the project is now a collaborative effort involving the CMI, the Andlinger Center, the Princeton Environmental Institute, the Woodrow Wilson School and Princeton University’s central administration, as well as collaborators from the Environmental Defense Fund, The Nature Conservancy, the Natural Resources Defense Council, Exxon, and BP.

Jorge Sarmiento: A robotic observation system that researchers have deployed in the Southern Ocean is providing year-round measurements of carbon fluxes and is changing our understanding of the ocean carbon sink. Previous results had revealed that significant outgassing of carbon dioxide (CO2) in the region was occurring in wintertime, reducing the region’s net uptake of carbon. Researchers are now trying to determine if part of the change in uptake may be due to Southern Ocean circulation changes and surface warming in response to a shift in the regional climate over recent years.

Gabriel Vecchi: A modeling study indicates that the urbanization of Houston acted to enhance the flooding from Hurricane Harvey (2017) in the city, both because less of Harvey’s rainfall was able to infiltrate the soil due to an increase in impervious surface coverage and because the increased surface “roughness” of the urban landscape acted to locally enhance Harvey’s rainfall. An observed 28-year increase in rapid intensification rates of North Atlantic hurricanes is unusual and may already include a signal from human radiative forcing; however, uncertainties in the hurricane data record over the rest of the world preclude a confident assessment of recent changes in rapid intensification. A modeling study indicates that explosive volcanic activity, such as the 1963 Mount Agung eruption, could impact global tropical cyclone (TC) activity in the years that follow, but that the response will be fundamentally different for different volcanoes. The goal of this work is to improve the understanding of the mechanisms behind and limits to the predictability of TC activity over the past few and next centuries. The work connects to broad questions in the climate science community, such as uncertainty over what TC changes are likely to occur over the coming century, and the extent to which intrinsic climate variability and natural forcing may be dominant over the impact of greenhouse forcing.

Brandon Reichl: Breaking waves induce bubbles of air in the upper part of the ocean that enhance air-sea gas exchange. This research utilizes new theory, data, and model simulations to quantify the contribution of bubbles to the air-sea CO2 flux in a global context. Our results indicate that bubbles contributed roughly 40% of the total air-sea CO2 flux over the timeframe 1982–2015, indicating they play a critical role in this important process.

Howard Stone: Climate changes involve atmospheric motions, ocean flows, and evolution of ice on land and in the sea. These dynamics are closely interrelated; insights into individual processes can help to illuminate poorly understood aspects of global climate dynamics, such as factors affecting the maintenance of sea ice cover in the Arctic basin. Sea ice cover can impact fresh water fluxes, local ecology, and ocean circulation. The Stone group is providing simplified models for understanding the movement and distribution of ice during the formation of polynyas, which refer to localized regions of water surrounded by ice, and through narrow straits, which can affect flow, mixing, and ecology in the ocean. The approach seeks to draw generalizations valid for various geometric and climate conditions.

Soil Carbon Group (Ian Bourg, Amilcare Porporato, Howard Stone, and Xinning Zhang): The objective of this project is to understand a key control on the stability of soil carbon: its protection by fine-grained minerals. Field experiments suggest that roughly half of the organic carbon present in soils is protected from microbial respiration by certain fine-grained minerals, but the mechanism of this mineral protection remains unknown. The Bourg, Porporato, Stone, and Zhang groups are using a unique combination of experimental and simulation approaches, spanning spatial scales ranging from molecules to landscapes, to elucidate this mechanism. These results will enable more accurate Earth System Model predictions of soil carbon dynamics and inform practical strategies for enhancing the soil carbon sink.

Methane Group (Xinning Zhang, Elena Shevliakova, and Vaishali Naik): Methane (CH4) is the second most important anthropogenic climate forcer after CO2. Atmospheric methane has risen to levels roughly 150% above preindustrial concentrations due to human activities and continues to rise despite a short period of stabilization during 1999-2006. Since the amount of methane in the atmosphere reflects the balance of chemical and biological processes that produce and consume the gas, efforts to decipher current trends and assess future emissions necessitate accurate accounting of different methane sources and sinks, as well as a clear understanding of their variability across temporal and spatial scales. These remain fundamental challenges for the scientific community. Since 2017, CMI has supported three complementary projects that address the largest unknowns in methane cycling: one experimental project focuses on the critical issue of wetland methane emissions (Project 1), and two global-scale modeling projects aim to quantify the individual sources, sinks, and variations of methane associated with land (Project 2) and the atmosphere (Project 3).

Michael Celia: In the past year, the Deep Subsurface research group has developed a research strategy focused on carbon capture and storage (CCS) opportunities in the United States, China, and India. For each, a targeted project has been identified, consistent with the current state of development in each location.

Daniel Steingart: Recent research findings by the Steingart group indicate that a lithium ion battery may be charged considerably faster and with minimal degradation if the charging is done at a higher temperature than usually considered (40 ̊C to 50 ̊C).