MET 12 Global Climate Change – Lecture 8 Radiative Forcing Shaun Tanner San Jose State University Outline GHG/Aerosols Radiative Forcing Activity 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. MET 112 Global Climate Change

Climate Change: how much and in what direction? 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.

MET 112 Global Climate Change That there is a link between CO2 and global temperatures is irrefutable as this diagram shows, but exact details of the link and all the possible feedback mechanisms are not clear. The interaction of positive and negative feedback effects associated with the greenhouse effect is currently a critical issue for the scientific community. MET 112 Global Climate Change

Anthropogenic Forcing Without doubt, humans have altered the radiative balance of the Earth system. The changes can be partitioned into the following categories: Enhanced greenhouse gases CO2, CH4, N2O, CFC’s Ozone Tropospheric Stratospheric Aerosols (Natural and Anthropogenic) Sulfate Carbon Biomass burning (black carbon) Land Use Changes First part of today’s lecture

Atmospheric Aerosols Microscopic liquid/solid particles Natural sources - examples Volcanoes (sulfur) Fires, dust Dust, sulfate particles reflect incoming sunlight: ___________________ Smoky soot absorb incoming sunlight: ____________________

Atmospheric Aerosols Microscopic liquid/solid particles Natural sources - examples: Volcanoes (sulfur) Fires, dust Dust, sulfate particles reflect incoming sunlight: ___________________ Smoky soot absorb incoming sunlight: ____________________ Cool atmosphere Warm atmosphere

MET 112 Global Climate Change

MET 112 Global Climate Change

Aerosols (II) Natural sources include: Dust, sea salt and volcanic emissions Anthropogenic sources include Automobiles, factories and biomass burning. Biomass burning: Anthropogenic portion: burning of large forests for agriculture Aerosols have ‘short’ relative lifetimes They can ‘float’ around for a few days to a week or two. Aerosols affect the Earth’s energy balance by reflecting incoming energy and/or absorbing incoming shortwave and longwave radiation. Cooling influence is stronger

Aerosols (III) There are three major types of aerosols Sulfate aerosols Black carbon aerosols Organic carbon aerosols

Aerosols (III) There are three major types of aerosols Sulfate aerosols Black carbon aerosols Organic carbon aerosols All have been increasing in concentration over the last 150 years – the industrial revolution.

Aerosol Observations from NASA Satellite That there is a link between CO2 and global temperatures is irrefutable as this diagram shows, but exact details of the link and all the possible feedback mechanisms are not clear. The interaction of positive and negative feedback effects associated with the greenhouse effect is currently a critical issue for the scientific community.

MET 112 Global Climate Change That there is a link between CO2 and global temperatures is irrefutable as this diagram shows, but exact details of the link and all the possible feedback mechanisms are not clear. The interaction of positive and negative feedback effects associated with the greenhouse effect is currently a critical issue for the scientific community. MET 112 Global Climate Change

That there is a link between CO2 and global temperatures is irrefutable as this diagram shows, but exact details of the link and all the possible feedback mechanisms are not clear. The interaction of positive and negative feedback effects associated with the greenhouse effect is currently a critical issue for the scientific community.

Sulfate Aerosols Natural source: volcanoes Anthropogenic sources: burning of fossil fuels 90% of sulfur aerosols are anthropogenic Example: SO2 (sulfur dioxide) From coal combustion Sulfate aerosols increasing globally Sulfate aerosols reflect incoming solar radiation. Total effect on Earth’s energy budget Cooling Radiative Forcing: negative

Black Carbon (Aerosols) Natural source: Natural biomass burning Anthropogenic source incomplete combustion from coal and diesel engines; biomass burning Also know as - ‘Elemental Carbon’ or ‘soot’ Black carbon absorbs solar radiation It’s black so has a low albedo (can also affect snow when it falls to the ground). Potentially harmful if inhaled. Total effect on Earth’s energy budget Warming Radiative Forcing: positive

Organic Carbon (Aerosols) Natural source Natural biomass burning Anthropogenic source Burning fuel Biomass burning Produced as a result of incomplete combustion. These aerosols are reflective Total effect on Earth’s energy budget Cooling Radiative Forcing: negative

Indirect Effect due to aerosols (I) Certain aerosols may enhance cloud production and character Recall how clouds form Water vapor condenses to liquid water This processes requires ‘cloud condensation nuclei’ Examples of cloud condensation nuclei Dust, salt, smoke (all of which are natural aerosols) So, aerosols (with both natural and anthropogenic origin) may serve as cloud condensation nuclei.

Indirect Effect due to aerosols (II) More cloud condensation nuclei would enhance cloud production The question then is how would clouds change Current understanding is that This processes would increase cloud albedo This idea of enhanced cloud formation by increases in aerosols is termed The ‘indirect effect’ of aerosols Understanding of these processes is currently incomplete. But model results suggest more low clouds and thus Total effect on Earth’s energy budget Cooling Radiative Forcing: negative

Over the last 250 years, CO2 concentrations have increased Over the last 250 years, CO2 concentrations have increased. The earth’s surface would therefore Receive more energy resulting in warming Receive less energy resulting in cooling Stay the same

Over the last 250 years, organic carbon aerosol concentrations have increased. The earth’s surface would therefore Receive more energy resulting in warming Receive less energy resulting in cooling Stay the same

Over the last 250 years, black carbon aerosol concentrations have increased. The earth’s surface would therefore Receive more energy resulting in warming Receive less energy resulting in cooling Stay the same

Over the last 250 years, the earth’s albedo has changed as a result of deforestation. The earth’s surface would therefore Receive more energy resulting in warming Receive less energy resulting in cooling Stay the same

Over the last 250 years, the amount of low clouds in the atmosphere has increased. The earth’s surface would therefore Receive more energy resulting in warming Receive less energy resulting in cooling Stay the same

Over the last 250 years, the intensity of the sun’s incoming radiation has increased. The earth’s surface would therefore Receive more energy resulting in warming Receive less energy resulting in cooling Stay the same

Over the last 250 years, aircraft induced high clouds have increased Over the last 250 years, aircraft induced high clouds have increased. The earth’s surface would therefore Receive more energy resulting in warming Receive less energy resulting in cooling Stay the same

Radiative Forcing A change imposed upon the climate system which modifies the Earth’s energy (radiative) balance. Radiative forcing is usually given in units of watts per square meter (W/m2), Positive values of radiative forcing contribute to heating of the surface, Negative values of radiative forcing Contribute to cooling of surface.

Figure 3.38 Earth’s annual energy budget Bloom-Fig-03-38-0.jpg

Radiative Forcing Examples of radiative forcing mechanisms include Changes in solar intensity Volcanic activity Changes in atmospheric composition CO2 Aerosols Ozone Changes in land surfaces

Radiative Forcing Changes in these mechanisms produce changes to the earth energy budget. The magnitude of the radiative forcing determine how strong the effect is. Radiative forcing is computed by comparing Pre-industrial energy balance (1750) with today’s energy balance (2000) 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.

Enhanced Greenhouse Gases Greenhouse gas concentrations have increased over the last 150 years dramatically The main anthropogenic contribution to greenhouse gases concentrations include: CO2, CH4, N2O, CFC’s (Halons) Increases in greenhouse gas concentrations are well observed

Enhanced Greenhouse Gases Greenhouse gas concentrations have increased over the last 150 years dramatically The main anthropogenic contribution to greenhouse gases concentrations include: CO2, CH4, N2O, CFC’s (Halons) Increases in greenhouse gas concentrations are well observed Radiative Forcing: positive 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.

Ozone Radiative Forcing: negative Radiative Forcing: positive Ozone exists in upper atmosphere Ozone layer (stratospheric ozone) Ozone layer protects the earth from harmful UV radiation Ozone layer responsible for heating the stratosphere Stratospheric ozone levels have been declining over last 20 years (ozone depletion) Radiative Forcing: negative Ozone exists in lower atmosphere Tropospheric ozone is another word for ‘smog’ Tropospheric ozone levels have increased over last 50 years. Radiative Forcing: positive 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).

Ozone 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). 34 34

Land Use Change Changes in the land use have contributed to Albedo changes Deforestation has been largest contributor High latitudes have been most affected Pre Industrial: Snow covered forests (low albedo) Current: Open snow covered areas (high albedo) Radiative Forcing: negative

Figure 4.27 Changes in global forcing in W m–2 by different factors from 1750 to 2005 Bloom-Fig-04-27-0.jpg

Radiative Forcing from the IPCC 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).

Radiative Forcing from the IPCC 1 2 3.0 3 4 5 -1.4 6 7 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 8 9 10

Radiative Forcing from the IPCC What does this part of the diagram mean?

Radiative Forcing from the IPCC What does this part of the diagram mean? Increases between 1750 through today have caused a 1.66 Watts per meter squared increase in the earth’s radiation budget. This by itself would warm the earth’s surface. Radiative forcing = 1.49 – 1.83 (average is 1.66)

Example Imagine you and your partner get offers to work for a new progressive company. They use a pay scale with ‘incentives’. You will get paid: $35,000  5,000 depending on your performance and your partner will get paid $75,000  60,000 . Calculate you and your partner’s total salary. The total (combined) salary is with no ‘incentives’: Your salary ranges from Your partner’s salary ranges from Maximum possible salary: Minimum possible salary: So, the total salary is between Big uncertainity! 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.

Example Imagine you and your partner get offers to work for a new progressive company. They use a pay scale with ‘incentives’. You will get paid: $35,000  5,000 depending on your performance and your partner will get paid $75,000  60,000 . Calculate you and your partner’s total salary. The total (combined) salary is with no ‘incentives’: = $110,000 Your salary ranges from $30,000 to 40,000 Your partner’s salary ranges from $15,000 to 135,000 Maximum possible salary: $175,000 Minimum possible salary: $45,000 So, the total salary is between $45,000 – 175,000 Big uncertainity! 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.

Terms in the radiative forcing diagram Term 1-2: Increases in CO2, CH4, N2O and CFCs Term 3: Decreases in upper atmospheric ozone (ozone depletion) Increases in lower atmosphere ozone Term 4: Increases in water vapor (due to extra CH4) Term 5: Changes in Albedo Increases in black carbon: Increase in surface albedo (deforestation): Term 6: Increases in sulfate aerosols

Terms in the radiative forcing diagram Term 1-2: Increases in CO2, CH4, N2O and CFCs producing warming (positive) Term 3: Decreases in upper atmospheric ozone (ozone depletion) provide less heating of upper atmosphere (negative) Increases in lower atmosphere ozone produce warming (positive) Term 4: Increases in water vapor (due to extra CH4) Term 5: Changes in Albedo Increases in black carbon: produce warming (positive) Increase in surface albedo (deforestation): produce cooling (negative) Term 6: Increases in sulfate aerosols produce cooling (negative)

Terms in the radiative forcing diagram Term 7: Increases in aerosols altering cloud properties (more low level clouds) Term 8: Increases in aircraft induced high clouds (contrails) Term 9: Increases in the strength of the sun produce warming (positive) Term 10-11: Increases in aircraft induced high clouds (contrails and cirrus clouds) Term 10: Total anthropogenic forcing

Terms in the radiative forcing diagram Term 7: Increases in aerosols altering cloud properties (more low level clouds) produce cooling (negative) Term 8: Increases in aircraft induced high clouds (contrails) produce warming (positive) Term 9: Increases in the strength of the sun produce warming (positive) Term 10-11: Increases in aircraft induced high clouds (contrails and cirrus clouds) Term 10: Total anthropogenic forcing Produce warming (positive)

Activity Calculate the total mean radiative forcing from the provided figure of individual radiative forcing from the IPCC. Please show your work! Calculate the total range of possible values from the above calculation. What conclusions does the total mean radiative forcing tell us about how the climate has changed? How does the range of values (or uncertainties) affect our above conclusions? So, the idea now is to add up all the terms and all the uncertainties to get the total radiative forcing. Your final answer for 1 and 2 will be something like: Mean: 3.3 W/m2 with a range from –0.3W/m2 to +4.5W/m2.

What is the total radiative forcing? Between -5 and -3 W/m2 Between -3 and -1 W/m2 Between -1.0 and -0.1 W/m2 Between 0 and 1.0 W/m2 Between 1.0 and 2.0 W/m2 Between 2 and 4 W/m2 Between 4 and 6 W/m2

Q2: What is the maximum radiative forcing Between -5 and -3 W/m2 Between -3.0 and -1.0 W/m2 Between -1.0 and -0.1 W/m2 Between 0 and 1.0 W/m2 Between 1.0 and 2.0 W/m2 Between 2 and 4 W/m2 Between 4 and 6 W/m2

Q2: What is the minimum radiative forcing Between -5 and -3 W/m2 Between -3.0 and -1.0 W/m2 Between -1.0 and -0.1 W/m2 Between 0 and 1.0 W/m2 Between 1.0 and 2.0 W/m2 Between 2 and 4 W/m2 Between 4 and 6 W/m2

Q3: What conclusions does the mean forcing tell us Warming forcing outweighs cooling Cooling forcing outweighs warming Human induced warming is much stronger than naturally forced warming. Both 1 and 3 Both 2 and 3

Q4: What conclusions does the range of radiative forcing tell us The warming forcing is more certain than the cooling. The cooling forcing is more certain than the warming. The earth should be warming, but by how much is difficult to say because of the uncertainty of the cooling factors. The cooling is stronger than the warming and thus the earth should cool. Both 1 and 3 Both 1 and 4 Both 2 and 3 Both 2 and 4