Geography 3, Lecture 23
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1) Climate forcing starts the process of climate change by creating an energy imbalance. In the case of anthropogenic climate change, it is a net positive radiative forcing due to the combined effects of greenhouse gases, so we have energy surplus. 2) Feedbacks take over from there. Positive feedbacks amplify the effects of the forcing. Negative feedbacks reduce the effects of the forcing. i)A positive feedback leads to even greater imbalance. ii) A negative feedback brings the system back into balance.
Why have human activities caused a positive climate forcing in tropospheric ozone (O3), and a negative forcing in stratospheric ozone?
1) Driving cars causes excess ozone in the troposphere (ozone pollution). Ozone is a greenhouse has that traps heat in the troposphere. 2) Human activities (CFCs) have destroyed stratospheric ozone ("ozone hole"). Ozone in the stratosphere absorbs solar radiation, so less of it leads to less energy being absorbed.
Methane (CH4) Nitrous oxide (N2O) Others
1) Is released from natural gas leaks, agriculture livestock and landfills. 2) Is released from agriculture, fossil fuel combustion, and biomass burning (slash+burn). 3) others include halocarbons that have been used for refrigerants and aerosol spray propellants.
La Nina vs. El Nino Energies
1) La Nina means more energy going into the ocean. 2) El Nino means more energy going into the atmosphere
Classify each of these effects of climate change as creating a positive or negative feedback. 1) A Earth's climate warms, ice sheets and glaciers start to melt. 2) As Earth's climate warms, the atmosphere can hold more water 3) Anthropogenic aerosols emitted during fossil fuel combustion act to increase the condensation of water vapor in the atmosphere, causing more clouds. 4) Increasing CO2 concentration has a "fertilizing" effect on forests, causing more trees to grow.
1) Positive (reduce albedo, greater imbalance). "ice-albedo feedback" 2) Positive (stronger greenhouse effect, greater imbalance "water-vapor feedback") 3) Negative (increase albedo with more clouds, bring back to balance). "Aerosol indirect effect" 4) Negative (reduces CO2 levels and greenhouse effect) "CO2 fertilization effect"
Other Climate Forcings
1) Positive forcing causes warming 2) Negative forcing causes cooling 3) CO2 has the largest climate forcing. Methane (CH4), nitrous oxide (N2O), halocarbons (CFCs) and ozone (O3) are also greenhouse gases. 4) Aerosols are tiny particles in the air. Sources include industrial combustion
IPCC Reports and Climate Projections
1) The IPCC 5th Assessment shows different temperature and sea level scenarios for different CO2 emissions scenarios.
Where is warming the most intense? Where is warming the least intense? Why?
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Review: Climate Change
El Nino Southern Oscillation (ENSO) as one of the dominant modes of climate variability (2-3 years)
Climate Models
Integrate everything that we know about climate forcing and feedbacks, as well as natural climate variability (pass of energy back and forth between atmosphere and ocean). 1) Models with anthropogenic forcing can re-create the observed temperature changes. 2) Models without anthropogenic forcing cannot. 3) Natural climate variability is important on 10-20 year timescales.
Another feedback involves the release of methane (CH4) from frozen lakes and tundra (permafrost) as the Arctic warms. Methane is a potent greenhouse has. Is this feedback positive or negative?
Positive feedback
Natural vs. Anthropogenic Radiative Forcing
anthropogenic forcing >> natural forcing
Which of the following is an indicator of climate change? a) It will be cold and rainy in SB this Thanksgiving b) The 2018 Pacific hurricane season was the most active on record c) SB experienced a 5yr drought from 2011-2016 d) Arctic sea ice extent has been declining over the past 40 years
d) Arctic sea ice extent has been declining over the past 40 years