Climate-Vegetation Interactions Flashcards
What were the dominant controls/limitations to vegetation growth globally? Nemani et al., 2003
- Temperature (33%) - limits growth in high northern latitudes
- Solar radiation (27%) - primarily limiting in tropics
- Water availability (40%) - primarily in Africa and Australia
- How will the future change in climate affect these controls?
What region has been most affected by increases in temperature?
Northern hemisphere - high latitudes
What may be some of the reasons for amplified warming in the high northern latitudes?
- Melting snow and ice - reveals darker water underneath - reduces albdeo - so less incoming radiation reflected - more radiation is absorbed - so amplifies warming
- Atmospheric / ocean circulation changes?
- Location of climate forcing - most emissions have been in northern hemisphere - greenhouse gases well mixed throughout world but aerosols are not - non-uniform distribution of aerosols may be a reason?
How are seasonal cycles of CO2 different in somewhere such as Mauna Loa or southern hemisphere sites compared to northern hemisphere sites?
Sites in NH (e.g., Barrow - Alaska) have much greater seasonal cycle of CO2 compared to other sites
- Source of carbon in winter, sink during summer
- Curve - amplitude - can observe change in photosynthesis and change in respiration
- Amplitude (difference between min and max CO2) of seasonal cycle has been increasing since 1960s - particularly
What may this increase in seasonal amplitude suggest about CO2 and reasons for this?
It suggests that there is a greater difference between the amount of carbon being taken up and amount of carbon being released by the biosphere
- Suggests that temperate and boreal forests have become more active during the growing season (more take up)
What technique could / has been used to look at the greening of the north? Myneni et al., 1997
Optical remote sensing of vegetation
- Normalized difference vegetation index (NDVI)
- Detects change in wavelengths - between 0 and +1
What has been shown about the greening of the north through multiples studies in many decades?
1981-1991: Showed increase in NDVI most seen between 45N-70N - suggested to be due to increased temperatures - extending growing season - grow for longer
1982-2011: Observed increase in NDVI has continued across Arctic Tundra but not so much over Boreal forest - greening continued but changed a bit
1981 - 2015: - 100 locations (Higgins et al., 2023) : combined NDVI and dynamic plant model
- Showed that greening only increased up to mid 2000s - but now potentially browning - decrease in NDVI value - >50% of sites showed same pattern
- Shows how enhancements that we thought were going on are now flipping
- Temperature and moisture trends dominate vegetation activity response
What elements of the ecosystem affect the carbon, energy and water balance?
Carbon balance::
- Photosynthesis
- Respiration
Energy balance:
- SW radiation (solar)
- LW radiation - reflected
- Albedo
- Sensible heat - outward
Water balance:
- Evapotranspiration
- Runoff
Relative strength of these effects determines overall impact on temperature - so if we change vegetation (e.g., deforestation) - we see changes in all these fluxes ^
What did idealised models about forest loss tell us about change in climate - Bala et al., 2007?
CO2:
Increase in CO2 in all cases with deforestation
Temperature:
- Increased in tropical regions
- Around standard (as if no deforestation) for temperate
- Decrease in temp for boreal - due to albedo effect - means more snow can accumulate and reflect heat - very strong effect
How have biogeophysical and biogeochemical effects impacted temperature due to land use change? Pongratz et al., 2010
- Biophysical (energy and water): cooling effect
- Biogeochemical (carbon): net warming effect
- Overall net effect on temperature - is warming - so biogeochemical effect dwarfs other effects - but not spatially uniform
What is LUMIP? Boysen et al., 2020
Land use model intercomparison project:
- Lots of people coming together to run their different models on how land use changes in future
- But models were still very different - not uniform
- Biogeophysical - cooling in high latitude - NH - albedo - but may change in future due to changes in evapotranspiration
What did study about converting cropland to forests over 50 year period show about the biogeochemical, biophysical and net effect? Arora et al., 2011
- Biogeophysical effects (energy and water) - warming effect
- Biogeochemical (carbon) - cooling effect
- Net effect on temp - cooling effect
Summarise the African Sahelian drought ecosystem-climate feedback
- Loss of vegetation (due to overgrazing) - increase in surface albedo
- Reduction of absorbed solar radiation and net radiation
- Cooling surface climate
- Promotion of subsidence of air aloft
- Subsidence decreases cloud formation and convection
- Decrease in rainfall
- So has positive feedback effect - lose even more vegetation
How could biome shifts? Give example and what effect might it have?
Biome shifting north - e.g., in north america
Climate feedback loop:
- Increased vegetation - lower albdeo - more productive vegetation - melting ice - feedback on darker surface
- Increase in vegetation = more water vapour in atmopshere = more warming
- And increased temperature will drive melting ice etc… complicated
