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Open Posted By: highheaven1 Date: 21/10/2020 Graduate Case Study Writing

 

1. Calculate the best estimate of the total radiative forcing from the provided figure of individual radiative forcings from the IPCC (see slide 37 of Lecture 8). Hint: You don’t need to include the “net anthropogenic” term when conducting this calculation. Please show your work. (3 points)

2. Calculate the range of possible values for the total radiative forcing. Please show your work. (3 points) 

3. What conclusions does the total radiative forcing tell you about how the climate has changed? Use 2-4 sentences for your response. (2 points)

4. How does the range of values (or uncertainties) affect the above conclusions? Use 2-4 sentences for your response. (2 points

Category: Arts & Education Subjects: Education Deadline: 12 Hours Budget: $120 - $180 Pages: 2-3 Pages (Short Assignment)

Attachment 1

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METR 112 Global Climate Changes – Lecture 8

Aerosols and Radiative Forcing

With More on Ozone Depletion

Henry Bartholomew (M.S.)

San Jose State University

Outline

Atmosphere

Ozone Layer

Aerosols

Radiative Forcing

Reading: Chapter 4, pages 19-29; Chapter 11, pages 21-24

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The primary goal of the concept of radiative forcing is to quantify all the factors that have contributed to our changing climate including the increases in greenhouse gases, increases in aerosols, ozone increases in the troposphere and decreases in the stratosphere, and changes in the sun.

Radiative Forcing: What is it?

A value for quantitatively determining a forcing’s effect on climate

The greater the magnitude of the value, the larger the warming/cooling effect

Positive values indicate warming

Negative values indicate cooling

We have studied the various factors that contribute to climate change. Some of these contribute to warming the climate Some of these contribute to cooling the climate  It would be helpful if we could develop a tool for measuring the strength of the various warming and cooling factors.  The Radiative Forcing calculation is a tool for measuring how climate will change due to a particular forcing mechanism.

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Forcing Factors: Warming or Cooling?

Some forcing factors have a warming effect on climate

Examples: Increases in greenhouse gas concentration, increases in sunspot activity

Others have a cooling effect on climate

Examples: Aerosols, stratospheric ozone decrease

Atmospheric Layers

Ozone layer absorbs ultraviolet radiation, with greater efficiency in the upper region of the stratosphere (more warming)

While temperatures usually decrease with height in the troposphere, they increase with height in the stratosphere

This is due to the presence of the ozone layer – it absorbs ultraviolet radiation, with greater efficiency in the upper region of the stratosphere (more warming)

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Stratospheric Cooling

While the troposphere is warming over time, the stratosphere may be cooling over time

While the evidence is clear that the troposphere is warming over time, due to increases in anthropogenic greenhouse gases (more proof of this in the radiative forcing diagram later), the stratosphere may be cooling over time

More uncertainty about stratosphere than troposphere

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Ozone Layer Depletion

Over time, the amount of ozone in the stratosphere has decreased, due to increases in CFC’s (chlorofluorocarbons)

Chemicals that contain carbon, chlorine, hydrogen, and fluorine

Chlorine breaks the O3 molecule into O and O2

CFC’s can originate from refrigerants, aerosol sprays, cleaning solvents, and bubbles in foams

Depletion of Ozone became important topic in 1970’s and 1980’s

“The Montreal Protocol on Substances that Deplete the Ozone Layer (a protocol to the Vienna Convention for the Protection of the Ozone Layer) is an international treaty designed to protect the ozone layer by phasing out the production of numerous substances that are responsible for ozone depletion. The treaty was opened for signature on September 16, 1987…As a result of the international agreement, the ozone hole in Antarctica is slowly recovering. Climate projections indicate that the ozone layer will return to 1980 levels between 2050 and 2070.”

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8

Lysol Foaming Disinfectant Cleaner

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Ozone Layer Depletion

Ozone Layer Depletion: Why Antarctica?

Chlorine breaks up from CFC’s more easily at colder temperatures

The presence of polar stratospheric clouds helps speed up the chemical reactions that remove chlorine from CFC’s

Winter time in stratosphere over Antarctica is cold and dark.

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Stratospheric Cooling

One reason that the stratosphere may cool is due to a decrease in ozone concentration

Another is due to an increase in anthropogenic greenhouse gases

As CO2, CH4, N2O, and other greenhouse gas concentrations go up, less outgoing infrared radiation reaches stratosphere to be absorbed

Ozone absorbs UV radiation, heating the stratosphere up.

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Aerosols

Microscopic solid or liquid particles suspended in the atmosphere, ranging in size from about 0.01 to 10 micrometers

Can act as CCN (meaning?)

Also alter the earth’s radiation budget, through their direct and indirect effects

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Aerosols

Short atmospheric lifetime, on the order of days to a couple weeks (in the troposphere)

Can stay in the stratosphere for a few years

Can then go back into ground or ocean

Can then go back into ground or ocean

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Aerosol Examples

Dust

Smoke (Sulfate, Black Carbon, Organic Carbon)

Salt

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MET 112 Global Climate Change

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MET 112 Global Climate Change

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Pollution

In our atmosphere, we usually “see” pollution as large clusters of aerosols

Humans can’t see greenhouse gases

Mention how natural gas burning is cleaner than coal and oil burning

Example: LA buses

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Aerosol Direct Effect

Can reflect shortwave radiation

Can absorb shortwave radiation

Can absorb longwave radiation

In general, the net effect of aerosols on the energy budget is cooling

Unlike greenhouse gases, aerosols can interact with both shortwave and longwave radiation

There is more uncertainty of the effects of aerosols on climate (compared to greenhouse gases)

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Aerosol Direct Effect

Aerosols

As a result of human activities, they have increased in concentration since the mid 1800’s (Industrial Revolution)

Why?

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Aerosols: Two Indirect Effects

First Indirect Effect:

Increasing anthropogenic aerosols cause a decrease in droplet size (Twomey 1974), resulting in a brighter cloud (higher albedo).

Cooling Effect

Radiative Forcing: Negative

Second Indirect Effect:

Reduced cloud droplet sizes cause a decrease in precipitation efficiency, a longer lasting cloud (Albrecht 1989), as well as a thicker cloud (Pincus and Baker 1994).

Sources of Aerosols

Natural sources include

Land (dust)

Ocean (salt)

Volcanic eruptions (smoke)

Anthropogenic sources include

Factories

Cars

Power plants

Deforestation

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Aerosol Observations from NASA Satellite

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Cedar Fire

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Interstate 5, near Pacific Beach

Largest wildfire in recorded California history

Burned 280,278 acres (438 square miles)

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Cedar Fire

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Sulfate Aerosols

Natural source: volcanoes

Anthropogenic source: burning of fossil fuels (hydrocarbons), such as coal and oil

The overwhelming amount (90%) of sulfate aerosols are anthropogenic

Example: SO2 released during coal combustion

Reflect incoming solar radiation.

Total effect on Earth’s energy budget

Cooling

Radiative Forcing: Negative

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SO2 combines with O2 to produce SO4^2-

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Black Carbon Aerosols

Natural source: biomass burning (such as forest fires)

Anthropogenic sources: incomplete combustion from coal and diesel engines, human-induced biomass burning (deforestation)

Also known as “Elemental Carbon” or “soot,” it is potentially harmful if inhaled

Absorbs solar radiation, due to a low albedo.

Total effect on Earth’s energy budget

Warming

Radiative Forcing: Positive

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Organic Carbon Aerosols

Natural source: Biomass burning

Anthropogenic sources: Fossil fuel burning, deforestation

These aerosols are reflective.

Total effect on Earth’s energy budget

Cooling

Radiative Forcing: Negative

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Produced as a result of incomplete combustion

Other Aerosols

Sea Salt

Comes from ocean (natural source)

Highly reflective (albedo up to 0.97)

Total effect on Earth’s energy budget

Cooling

Radiative Forcing: Negative

Dust

Comes from natural (soil, volcanic eruptions) and anthropogenic sources (homes, offices)

Uncertain effects on Earth’s energy budget

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Radiative Forcing

A change imposed upon the climate system which modifies the Earth’s energy (radiative) balance.

Usually given in units of Watts per Square Meter (W/m2).

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A way to quantify a forcing’s effect on climate

Positive values contribute to warming.

Negative values contribute to cooling.

Figure 3.38 Earth’s annual energy budget

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Bloom-Fig-03-38-0.jpg

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Radiative Forcing

Changes in individual forcings produce changes to Earth’s energy budget.

The magnitude of the radiative forcing determines how strong the effect is.

Radiative forcing is computed by comparing pre-industrial energy balance (1750) with today’s energy balance (2000)

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So, the idea of radiative forcing is like this. We want to compare the Earth’s energy budget today (2000) with preindustrial times (1750) and account for the changes in greenhouse gases, aerosols, ozone amounts and solar variations.

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Enhanced Greenhouse Gases

Greenhouse gas concentrations have greatly increased over the last 150 years

Radiative Forcing: Positive

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If we just consider increases in greenhouse gases (GHGs), then the additional GHGs in the atmosphere today compared with the year 1750 produce additional warming or cause an increase in the radiative forcing (positive value). We will see how large this is in a bit.

CO2: 280-400 PPM

CH4: 700-1800 PPM

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Ozone

Exists in the upper atmosphere

Stratospheric ozone levels had been declining from 1970 to 2010

Radiative Forcing: Negative

Exists in the lower atmosphere

Tropospheric ozone can mix with fog and/or haze to produce smog

Tropospheric ozone levels have increased over the last 50 years

Radiative Forcing: Positive

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As outlined above, changes in ozone cause both a positive and negative forcing due to the differences between tropospheric ozone (which is ozone that exists in the troposphere and that is produced mainly by automobile and factory emissions) and stratospheric ozone (which is our ozone layer).

Protocol will have prevented 2 million skin cases per year by 2030!

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Land Use Change

Changes in land use have contributed to albedo changes

Deforestation has been the largest contributor

High latitudes have been most affected

Pre Industrial: Snow covered forests (lower albedo)

Current: Open snow covered areas (higher albedo)

Large uncertainties exist in details of the changes

Radiative Forcing: Negative

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Radiative Forcing from the IPCC

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This is the ‘big’ radiative forcing diagram! It’s really a great summary of the science of climate change and it’s a widely cited and used tool for understanding the processes that influence today’s climate.

In this diagram, there are 13 separate forcing terms that are displayed. When we say forcing terms, we mean processes that influence (or force) the climate. The first one is due to increases in GHGs (CO2, N2O, CH4 and Halocarbons).

Radiative Forcing from the IPCC

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2

3

4

5

6

7

8

9

10

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This is the ‘big’ radiative forcing diagram! It’s really a great summary of the science climate change and it’s a widely cited and used tool for understanding the processes that influence today’s climate.

In this diagram, there are 13 separate forcing terms that are displayed. When we say forcing terms, we mean processes that influence (or force) the climate. The first one is due to increases in GHGs (CO2, N2O, CH4 and Halocarbons).

Avg is 1.6

Max is 1.83+1.08+0.7+0.3-0.4=3.4

Min is 1.5+0.86+0.1-0.4-0.9-1.8=-0.6

Radiative Forcing from the IPCC

What does this part of the diagram mean?

Increases in atmospheric CO2 concentration between 1750 through 2000 have caused about a 1.66 W/m2 increase in the earth’s radiation budget.

This term by itself would warm the earth’s surface.

Radiative forcing value is between 1.49 – 1.83 (average is 1.66)

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Example

Imagine that you and your friend get offers to work for a new environmental company. They use a pay scale with ‘incentives’. You will get paid $35,000  5,000 depending on your performance, and your friend will get paid $75,000  60,000. Calculate you and your friends’ total salary.

The total (combined) salary with no ‘incentives’:

$110,000

Your salary ranges from

$30,000 to $40,000

Your friend’s salary ranges from

$15,000 to $135,000

Maximum possible combined salary:

$175,000

Minimum possible combined salary:

$45,000

So, the total possible salary for you two is between

$45,000 and $175,000

Big Uncertainty!

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Simply take the GHG forcing and ozone depletion term and combine. First add the average values (the mean value (2.4+ (-0.1)) to get the combined radiative forcing, and then calculate the uncertainty or range of possible values. You can do this by adding the most positive value (2.6 and 0) with the most negative (2.2 and –0.2) to give you the range (2.0 to 2.6).

This now means that even though ozone depletion acts to cool the earth, combined with increases in GHGs will still cause the earth to warm. The enhanced GHGs are quite strong and overwhelm the cooling of ozone depletion.

Radiative Forcing from the IPCC

1

2

3

4

5

6

7

8

9

10

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This is the ‘big’ radiative forcing diagram! It’s really a great summary of the science climate change and it’s a widely cited and used tool for understanding the processes that influence today’s climate.

In this diagram, there are 13 separate forcing terms that are displayed. When we say forcing terms, we mean processes that influence (or force) the climate. The first one is due to increases in GHGs (CO2, N2O, CH4 and Halocarbons).

Avg is 1.6

Max is 1.83+1.08+0.7+0.3-0.4=3.4

Min is 1.5+0.86+0.1-0.4-0.9-1.8=-0.6