Land-atmosphere interaction (1): Vegetation feedback & global warming

1. Land-atmosphere interaction (1): Vegetation feedback & global warming John Banghoff Junior, Atmospheric Science

2. What is the Carbon Cycle?

3. Carbon Cycle Video • http://www.youtube.com/watch?feature=player_detailpage&v=U3SZKJVKRxQ

4. How does that relate to global warming and vegetation? • Concentration of CO2 is increasing in the atmosphere. This leads to global warming. • Plants take in CO2 during photosynthesis so they can help compensate for some of the increased CO2 – to a certain extent.

5. Carbon Sinks or Stores

6. Carbon-Vegetation Feeback • For 50 years, ecosystems have been absorbing 25-30% of anthropogenic carbon dioxide emissions (a majority in forest biomass and soils) • More CO2 leads to more plant growth, which leads to more CO2 uptake. • Warming temperatures lengthen growing season, thus lengthening CO2absorbtion.

7. The Big Question: HOW LONG CAN THESE CARBON SINKS KEEP UP WITH ANTHROPOGENIC PRODUCTION OF CO2?

8. Cox et al. 2000 • Investigation of climate simulations which take into account the effect of climate change on the carbon cycle feedback. • Three different simulations: • Fixed vegetation (standard simulation) • Interactive CO2 and dynamic vegetation (doesn’t include adjustment for climate change) • Fully coupled climate/carbon-cycle

9. SUCCESS!!!!! The figure shows the anomaly in the growth rate of atmospheric CO 2 versus the Nino3 index, taken from our pre-industrial control simulation (crosses) and the Mauna Loa observations (triangles). USED TO TEST THE ACCURACY OF MODELING OF ENSO TO DETERMINE VALIDITY OF FULLY COUPLED MODEL.

10. Land becomes a source by 2050 (approximately). • By 2100, land and ocean cancel each other out so emissions supply all of increased carbon concentration. Absence of climate forcing factors

11. Too high – no aerosol cooling. • Note increased temperature and CO2 concentration with fully coupled model. the fully coupled simulation with interactive CO2 and dynamic vegetation (red lines), a standard GCM climate change simulation with prescribed (IS92a) CO2 concentration and fixed vegetation (dot-dashed lines) and the simulation which neglects direct CO2-induced climate change (blue lines).

12. Note reduction of terrestrial carbon after 2050 as a result of climate driven loss of soil carbon. vegetation carbon soil carbon global land area (continuous lines) and South America alone (dashed lines).

13. Scary Stats from Coupled Model • Increase in CO2 concentration is 250 ppm higher (980 ppm) than the standard simulation. This equates to an 8 K increase from 1860-2100. • Model with fixed vegetation has 5.5 K increase. Model without climate change has 4 K increase.

14. Reichstein et al. 2013 • Discusses how terrestrial carbon sinks might actually be made less effective by extreme climate events. • Looks at forests, croplands, and grasslands. • Discusses extreme events that affect each of the aforementioned land coverage regions.

15. What affects Carbon Sinks? • Increased research that climate extremes can lead to a decrease in carbon stocks. • Examples include severe storms or periods of drought. • How extreme is enough to alter the ecosystem?

16. Extreme Climatic Events • “an episode or occurrence in which a statistically rare or unusual climatic period alters ecosystem structure and/or functions well outside the bounds of what is considered typical or normal variability” • Examples might include a combined heat wave and drought or a drought followed by heavy precipitation.

17. Processes and feedbacks triggered by extreme climate events. M Reichstein et al. Nature 500, 287-295 (2013) doi:10.1038/nature12350

18. Types of Effects • Concurrent Source – An event that puts CO2 into the atmosphere when it occurs. Ex: Fire • Concurrent Sink – An event that takes in CO2 or keeps it out of the atmosphere. Ex: Photosynthesis • Delayed Source – An event that eventually leads to increased CO2concentration. Ex: Plant death • Delayed Sink – An event that eventually leads to CO2storage. Ex: Sedimentation

19. Overview of how carbon flows may be triggered, or greatly altered, by extreme events. Gross Primary Productivity (GPP): the rate at which photosynthesis or chemosynthesis occurs. M Reichstein et al. Nature 500, 287-295 (2013) doi:10.1038/nature12350

20. Forests

21. Grasslands

22. Croplands • Highly influenced by human intervention. • Type of crop, amount of harvesting, time left bare. • Therefore, hardest to simulate and account for impacts on carbon dioxide store.

23. Global impact of extreme events on the carbon cycle. Extreme Temps Water Scarcity M Reichstein et al. Nature 500, 287-295 (2013) doi:10.1038/nature12350

25. Uncertainty Remains • Climate extremes seem to be occurring more frequently, but how frequent are they? • What effect do they have on the carbon-cycle and how do they contribute to feedbacks? • Further research must be done to investigate extreme climate events and how each part of the carbon cycle is contributing to feedbacks. • We must further improve weather forecasting and climate modeling to improve accuracy.

26. Uncertainty Remains • Carbon Cycle is still only partially understood. • How ocean, land, and vegetation sinks function is still not fully grasped. • Rate of CO2 increase depends on when the land will become a source instead of a sink. • Models don’t account for human impacts in deforestation or afforestation which can alter timing and functionality of sinks.

27. Let’s Dive Into the Models a Little Bit More Hasting Ng will have more in our next presentation investigating further the climate models and how they handle carbon-cycle feedbacks – specifically the role of ocean and land carbon sinks.

28. Questions, Comments, Concerns??