Red Hills Fire Festival

Many group members volunteered at the Red Hills Fire Festival at Tall Timbers Research Station. The event drew 900 attendees to the lawn of the historic Beadle House for prescribed fire demonstrations and exhibits about local ecology. Our group hosted a table with atmospheric science demonstrations, illustrating how fires can be detected from space and how to measure humidity, among other things.  

New NASA grant to join FIREX-AQ

NASA announced that our group will receive a grant to participate in the FIREX-AQ field campaign. FIREX-AQ aims to better quantify emissions from fires and monitor the chemical aging of smoke plumes. The campaign will use NASA and NOAA aircraft in summer 2019. Together with Dr. Henry Fuelberg, our group will provide weather, fire, and smoke forecasting for the flight planning team.

Kelly Graham wins NASA fellowship

Kelly was awarded a NASA Earth and Space Science Fellowship to continue her research on Arctic CO2 fluxes. She plans to analyze using O-Buoy and OCO-2 observations with the GEOS-Chem model to better understand the effect of changing sea ice on CO2 in the Arctic. The NESSF fellowship will support Kelly for 3 years. Congratulations!

New NASA grant to study fires

NASA awarded Holly and Chris a 3-year grant to study biomass burning in the Southeast US. The project will develop an improved inventory of fire emissions in the region and better understanding of their impacts on regional air quality and global climate. Research partners for the project include Tall Timbers Research Station and Land Conservancy and the Florida Department of Health.

Reduced air pollution has improved forest health

Ozone air pollution harms people and plants. Worldwide, exposure to ozone causes about 700,000 excess deaths each year, as well as impaired breathing, asthma attacks, and reduced crop yields. Changes in vehicle and industrial emissions in the United States required by the Clean Air Act have improved surface ozone air quality significantly in many urban and rural regions. In a recent letter to Nature, I show that these trends of falling ozone help explain some changes in the way forests use water that have been observed, but previously not fully explained. Trees take carbon dioxide from the atmosphere in order to photosynthesize sugars and biomass, but lose water through transpiration in the process. The ratio of carbon dioxide gained to water lost is water-use efficiency. Long-term measurements in many forests in North America and Europe have revealed that forests have increased their water-use efficiency over the last 20 years. Rising carbon dioxide levels in the atmosphere (due to fossil fuel use and deforestation) explain part of the water-use trend, but not all of it. Using empirical relationships between ozone and water use in controlled experiments on many tree species, I show that the ozone trends explain a significant part of the water-use efficiency trends. These ozone-water interactions should be added to future climate and biosphere models to better understand and predict how air pollution affects climate and the carbon and water cycles.

At rural sites throughout the Northeastern and Midwestern United States (left) surface ozone (O3) pollution has been falling for the last 15 years. Trees and crops injuries from ozone are related to their cumulative exposure to ozone over a season, which is measured as AOT40 (right). AOT40 has fallen 5% per year in the Midwestern US and 7% per year in the Northeastern US. These ozone trends explain about one-sixth of the trend in water-use efficiency that has been observed at nearby forest sites, which is more than can be explained by other factors.

Methane projections for the 21st Century

In a new paper in Atmospheric Chemistry and Physics, we present a new method for predicting atmospheric methane concentrations along any socioeconomic emission scenario. We use a simple and fast modeling approach that accounts for chemistry-climate interactions, including their uncertainties. Since rising greenhouse gas abundances are the main cause of recent climate change and methane is one of the most important greenhouse gases, these results will impact the predicted climate evolution in the 21st century.

Projected future atmospheric methane abundance (left) and lifetime in the atmosphere (right) in the RCP 8.5 socioeconomic climate and emission scenario. Projected uncertainty (shaded) accounts for uncertainty in the present-day budget, emissions, and chemistry-climate effects. We compare our projections to the MAGICC model and the IPCC Third Assessment Report (TAR) model, which do not include uncertainties.

Improved Methane Global Warming Potential (GWP)

Global Warming Potentials (GWPs) serve as an “exchange rate” among greenhouse gases, enabling emitters to compare the climate benefits of reducing emissions of different gases, such as carbon dioxide (CO2) or methane (CH4). The methane GWP is defined as the total radiative forcing (i.e. heating) over 100 years (or another time horizon) caused by emitting methane, compared to emitting an equal amount of CO2. Since methane is a precursor of ozone and stratospheric water vapor, both of which are greenhouse gases, the methane GWP customarily includes the radiative forcing caused by these decay products. Our analysis suggests that methane breakdown in the atmosphere produces more ozone and more radiative forcing than previously recognized, with most of the additional ozone residing in the stratosphere. New data also revise the methane lifetime upwards (9.1 yr). Taken together, we calculate the methane GWP to be 32, which is 25% larger than past assessments. This high GWP implies that methane emissions are more harmful to the climate than previously thought, but also that reducing those emissions will have greater benefits. Our full analysis of atmospheric methane lifetime, future abundances, and GWP is published in Atmospheric Chemistry and Physics.

GWP provides a basis for comparing climate heating caused by different greenhouse gases that have different absorbances (heat-trapping ability) and atmospheric lifetimes. Our work suggests that the methane GWP (100 yr) is 32, significantly larger than the value of 25 that that was recommended by the Intergovernmental Panel on Climate Change (2007).