Models

Question 1

What was found to be a major control (coupling) for predicting seasonal rainfall?

Answer 1

Soil moisture and vegetation
- Strong coupling of land-atmosphere
- Amount of moisture in soil good predictor for rainfall over next few weeks

Question 2

What impacts will land-use change have on global climate - Weber et al., 2024?

Answer 2

• Changing surface albedo
• CO2
• Aerosol and trace gases

Question 3

How might you develop and couple a climate model?

Answer 3

Vegetation cover -> Climate model (Land surface model + Atmospheric model) -> Climate
- Evolved so that vegetation is coupled with vegetation cover - so as vegetation cover changes - it can couple and feedback with different components

Question 4

Give an example of a land surface model in the UK

Answer 4

Joint UK Land Environment Simulator (JULES)

Question 5

Whar are the three communities and their models that contribute to land surface models?

Answer 5

Climate community
- Biophysical models - exchange of energy, water and momentun

Carbon community
- Biogeochemical models - modelling carbon exchange between different pools

Plant physiologists
- Biome models - modelling vegetation distribution and phenology according to plant physiology - ‘Dynamic Vegetation’ models

All contribute to generation of land surface models used in coupled climate-carbon simulations (CLM 4.0)

Question 6

How can you evaluate models - and give example?

Answer 6

• Use observations to evaluate models - to test to see if model is producing something close to reality
• Comparing will tell you what the model is doing wrong - and therefore you can know what to improve on

E.g., evaluating modelled evapotranspiration with observations:
- Amazon basin annual mean ET
- Spatial variability in ET
- Seasonal cycle in ET
- Simulated ET evaluated against satellite remote sensed and catchment balance ET

Question 7

How can we use models to understand the Greening of the Earth, and what was found?

Answer 7

Observed positive trend in Leaf Area Index (LAI) over last few decades - by what is causing greening?
- Run mulitple simulations with the same model - used to separate drivers of change: e.g., observations, CO2, climate, nitrogen, land cover change
- Found that CO2 increase over last few decades is the greatest driver - named: CO2 Fertilization Effect

Question 8

How does this Greening impact climate?

Answer 8

Zeng et al., 2017:
- Increased greening = increase evapotranspiration = increased surface cooling
- This has offset some of climate warming over last few decades - around 12%

Question 9

How big are carbon sinks around the world and how can you measure them?

Answer 9

~2.4 PgC/year - around 25% carbon offset
- Measure using carbon inventories - measure size of vegetation over time

Question 10

What is known about the land-carbon sink in the future?

Answer 10

Large disagreement in magnitude and sign of future land-carbon sink
- From CMIP5 results for different RCP scenarios
- Can split into vegetation and soil carbon

Question 11

Why is there such large uncertainty and change in sign in these land-carbon sink models?

Answer 11

• CO2 - positive effect - increase carbon uptake - greening
• Temperature - negative effect
• Depends on the dominance of each factor

Question 12

How can you measure vegetation response change in CO2?

Answer 12

FACE - Free air carbon dioxide enrichment
- Control CO2 conc in area of woodland and measure the impact
- Use wind to control CO2
- Will tell us how much forests actually respond to CO2

Question 13

What do long-term measurements indicate about carbon sinks in Amazon?

Answer 13

Habau et al., 2020:
- Carbon removal from increasing tree growth - with rising CO2
- But is offset by carbon losses driven by increased tree mortality
- But this does not appear to be happening yet in the Congo

Gatti et al., 2021:
- Vertical profiles of CO2 over the amazon
- Shown that deforestation and climate change driven Amazon forest to a net carbon source

Question 14

What are dynamic global vegetation models?

Answer 14

DGVM:
- Give model information on climate
- Model uses this information to decide is this place going to be a forest/grass etc
- As it develops - it models competition between these biomes

Question 15

What are the problems with DGVMs?

Answer 15

• If we let model simulate where vegetation is - will get that wrong - will introduce other errors into model - feedbacks on climate
• But is good for if you want to understand how the distribution of vegetation will change depending on climate - as DGVMs can alter where vegetation is

Question 16

What was one of the main reasons that caused a nonlinear climate tipping point in the Amazon? McKay et al., 2022

Answer 16

The change in rainfall

Question 17

What are ‘energy limited’ models and why are they important for modeling the Amazon?

Answer 17

Models that correctly capture P-ET and Rdn-ET interactions predict future P reductions in the Amazon
- Found that these models had bigger reductions in rainfall than the water limited models
- Comparison of models in - Baker et al., 2021
- So comparing energy vs water limited models is helpful for understanding what might be happening in the Amazon

Question 18

What is included in CMIP4 and CMIP5 models?

Answer 18

CMIP4:
- CO2
- Climate

CMIP5:
- Also land use change

Not included:
- Land-use/management details
- Nitrogen (deposition)
- Fire
- Permafrost

Question 19

What is the UKESM?

Answer 19

• First full simulation system for full earth system models - in UK
• To give better predictions for how earth will change in future