The Arctic Climate System
Our research group was recently awarded a three year National Science Foundation Grant (ATM-0641299) to study the global climate implications of Earth system change in the Arctic. This work makes extensive use of climate system models to evaluate the potential influence that high-latitude warming is having on Arctic terrestrial ecosystems and how biospheric changes may lead to amplification of the warming through biophysical and biogeochemical feedbacks. As part of this project, we are developing a new tundra vegetation type to account for the rapid migration of invasive shrub tundra species throughout the Arctic. This new vegetation type includes improvements to above ground biophysics and biogeochemistry as well as below ground carbon storage and takes into account changes in soil and permafrost changes due to rapid warming.
Summary - Significant climatic and terrestrial ecosystem changes are occurring in the Arctic in response to global warming. Over the last 25 years, satellite data indicate that the transition from grasses to shrubs is rapidly occurring in many tundra regions. On a longer timescale, repositioning of the boreal forest-tundra boundary may be expected as the forests shift northward to maintain an optimal growing environment. The observed and predicted greening-up of the Arctic region may result in large changes to both the global carbon budget and the Northern Hemisphere general circulation by way of complex biogeochemical and biophysical interactions between the vegetation and the atmosphere. Over the course of this century, warming is expected to increase an additional 4-7°C as greenhouse gas levels continue to rise. A rapid response to mitigating this global warming is dependent on informed policy decisions that are based on sound and relevant science of the global climate system.
The aim of this proposal is to put terrestrial ecosystem changes and the climate response into a global context where the changes are likely to affect the entire planet. The focus will be on changes in ecosystem carbon storage in the Arctic and the global implications of ecosystem changes through modification of the Northern Hemisphere general circulation. The goal is to understand the processes and interactions that link terrestrial ecosystem changes to the global climate. The proposed project is motivated by consideration of the potential, but previously not quantified, impacts that climate-driven change in Arctic terrestrial ecosystems are likely to have on the global climate.
Our group is evaluating the influence of changes to Arctic terrestrial ecosystems on the global climate by testing the following two hypotheses. First, it is not possible to predict a priori whether global warming and increasing atmospheric CO2 concentrations will lead to net carbon storage or loss in the Arctic without examining the competing effects of carbon fertilization, climate change, nutrient availability, and soil respiration together in a global climate modeling system and evaluating their relative contributions to the global carbon budget. Second, high-latitude warming and increasing atmospheric CO2 concentrations will alter the current distribution of Arctic terrestrial ecosystems and lead to changes in the surface and tropospheric energy balance, and the Northern Hemisphere general circulation.
These hypotheses are being evaluated using a state-of-the-art global climate system model, CCSM3-IBIS (and CCSM3 with CLM). To address the hypotheses, the model is being modified to include a better representation of Arctic terrestrial ecosystem response under elevated atmospheric CO2 concentrations and to improve soil and plant biogeochemistry processes of Arctic vegetation. Simulations are being run with the improved model to address the hypotheses and quantify the climate effects of Arctic terrestrial ecosystem changes by way of biophysical and biogeochemical processes. This work represents an important improvement of model-derived responses to Arctic land surface change and the feedbacks on the climate system as well as overall improvements of how vegetation, soil biogeochemistry, and the climate in the Arctic environment are modeled.
Impacts of this research will be achieved through three expected outcomes: (1) an improvement of Arctic terrestrial ecosystem biogeochemistry processes within the context of a global model, (2) an assessment of the effects of climate change and elevated CO2 on the Arctic terrestrial carbon budget and the individual components, and (3) an assessment of future high-latitude warming and increasing CO2-induced changes in Arctic terrestrial ecosystems and the effect on the Northern Hemisphere general circulation. The proposed represents the first quantitative analysis of the influence of Arctic terrestrial ecosystems on large-scale changes to the Northern Hemisphere general circulation and teleconnection processes. In this respect, it provides a long-needed bridge between the Arctic terrestrial community and the global climate community.
