EAE 15 - Climate Change

Question 1

How do volcanoes affect climate?

2 points.

Answer 1

Volcanic eruptions can affect climate but primarily act to cool the surface

• CO₂ emissions from volcanoes currently about 60-100 times smaller than those from fossil fuels
• Primarily a negative forcing in the short term due to aerosol release

_{EAE 18aa}

Question 2

What are aerosols?

Answer 2

Aerosols are small liquid or solid particles suspended in the atmosphere

They have a lifetime in the troposphere of 1 day - 2 weeks and their impact on climate depends on many factors

_{EAE 18ab}

Question 3

What affect do anthropogenic aerosols have?

Answer 3

Anthropogenic aerosols have had an overall cooling effect since pre-industrial

_{EAE 18ac}

Question 4

What is the impact of ozone?

2 points.

Answer 4

Impacts of ozone variations depend on location

• Ozone abundance is greatest in the stratosphere
• Ozone blocks between 97-99% of UV-B and UV-C radiation from reaching the surface

_{EAE 18ad}

Question 5

What is the ozone hole?

Answer 5

• Ozone depletion over Antarctica of more than 50% compared to 1980, plateauing during 2000s
• Stratospheric ozone depletion has only a minor impact on global surface temperatures (lets in more UV but also reduces the infrared trapped)
• Depletion occurs predominantly in austral spring months
• Recovery of the ozone hole is projected by mid-late 21st Century

_{EAE 18ae}

Question 6

What is ther impact of the ozone hole?

2 points.

Answer 6

• Little direct impact on global surface temperatures from the ozone hole
• But there is an indirect impact through changes on the Southern Hemisphere atmospheric circulation

_{EAE 18af}

Question 7

What is the impact of natural variablility?

3 points.

Answer 7

Natural internal variability of the climate system can change the rate of surface warming

• Natural cycles like El Niño only move heat from the atmosphere to the ocean or vice versa, otherwise they would violate conservation of energy.
• We know the atmosphere is warming so to balance that the ocean would need to be cooling
• But BOTH the atmosphere and ocean are warming

_{EAE 18ag}

Question 8

What is the observed termperature increase?

Answer 8

• Global surface temperatures incr by ~1.0ºC since 1900
• Almost the entire globe warmed between 1901 and 2012
  Multiple lines of robust and compelling evidence support the conclusion that many aspects of the climate system have changed

_{EAE 18ah}

Question 9

What are the observations in Australia?

2 points.

Answer 9

• Australian temperatures have risen by a about 1ºC, a similar amount to that of global temperatures
• Rainfall has declined in the south and increased in the north during their rainy seasons

_{EAE 18ai}

Question 10

Is human influence on the climate system clear?

2 points.

Answer 10

• It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century (IPCC AR5)
• Increased certainty since the IPCC AR4 from a combination of improved observations, models and scientific understanding

_{EAE 18aj}

Question 11

How do we project future climate?

3 points.

Answer 11

Future climate depends on:

• inherent variability
• social & economic choices
• response of the Earth system

→ use a scenario approach where a variety of potential pathways are examined

→ use comprehensive climate models as they are the best tools available for future projections

_{EAE 18ak}

Question 12

Why do we need more than one model?

3 points.

Answer 12

• Diversity of equally plausible approaches to modelling the climate system → no best model!
• Numerous modelling centres worldwide
• Attempts to link model performance to projections, for the most part, have proven difficult so multimodel distribution required

_{EAE 18al}

Question 13

What are some of the changes in quality of climate models?

6 points.

Answer 13

Compare 1980s, 1990s & mid 2000s

Resolution:

• 1980s = 500 km
• 1990s ≈ 200 km
• 2000s = 110 km

Factors:

• 1980s = Land, Clouds, Ice
• 1990s = add Volcanic activity, Sulphates & Ocean
• 2000s = add Chemisty and Interactive vegetation.

_{EAE 18am}

Question 14

How do scenarios change over time?

2 points.

Answer 14

By the end of the 21ˢᵗC

• Global temperatures are likely to exceed 1.5°C for all RCPs (except RCP2.6)
• Global temperatures are likely to exceed 2°C for RCP6.0 and RCP8.5

_{EAE 18an}

Question 15

What are carbon budgets?

5 points.

Answer 15

• Every ton of CO₂ causes about the same amount of warming, no matter when and where it is emitted
• To limit warming to likely less than 2°C from CO₂ alone, total emissions since preindustrial need to be limited to less than 1000 GtC
• Accounting for non-CO₂ forcing as in RCP2.6 reduces the allowed cumulative emissions to about 800 GtC
• About 530 GtC were emitted by 2011
• CO₂ emissions from permafrost or a higher likelihood require a lower budget

_{EAE 18ao}

Question 16

What was the average CO₂ in the atmosphere in 2017?

Answer 16

The global annual mean concentration of CO2 in the atmosphere in 2017 was ~405 parts per million

_{EAE 18ap}

Question 17

What is the increase in CO₂ by 2017?

Answer 17

A 46% increase since 1750 and higher than at any time in at least the past 2 million years

_{EAE 18aq}

Question 18

What is the dominant contributor to CO₂?

Answer 18

Emissions from burning fossil fuels continue to increase and are the dominant contributor to the observed growth in atmospheric CO₂

_{EAE 18ar}

Question 19

What was the Impact of COVID-19 pandemic on CO2 emissions?

Answer 19

Liu et al found that emissions dropped by 8.8% over the first six months of 2020 in comparison to 2019

COVID-19 is projected to lead to a 0.4 ppm drop in CO₂ concentrations in the atmosphere this year compared to previous projections for 2020 UK Met

_{EAE 18as}

Question 20

What is the projection of CO₂ concentrations as emissions change?

3 points.

Answer 20

• Zero CO₂ emissions lead to near constant surface temperature
• A large fraction of climate change persists for many centuries
• Depending on the scenario, about 15-40% of the emitted carbon remains in the atmosphere for 1000 years

_{EAE 18at}

Question 21

What is the impact of COVID-19 pandemic on temperatures?

2 points.

Answer 21

• Along with a decrease in GHG emissions, COVID-19 has also led to a drop in SO₂ emissions, which would normally cool the atmosphere.
• The net effect results in a negligible impact on global temperatures.

_{EAE 18au}