AOS 1 Final Exam

Changes in the global carbon cycle due to human activities

- Burning of fossil fuels alters the human emissions in the global carbon cycle. - Pre-industrial cycle was balance, but now there is human emissions into the atmosphere - More CO2 emitted into the atmosphere - Humans are removing carbon from the slow carbon cycle and putting it into the fast carbon cycle through the burning of fossil fuels - the fast carbon cycle is movement between land and the atmosphere where the slow carbon cycle happens over millions of years - Deforestation leads to more CO2 released

Decline in arctic sea ice, ice albedo feedback

- Extent of sea ice is closely linked to temperature, and has a strong seasonal cycle - Sea ice Albedo Feedback is a positive feedback (replacing high albedo of ice with a lower albedo of the open ocean) - Sea ice has a much higher albedo than water. The decline in sea ice strongly affects how much solar energy is absorbed by the surface. - Temp Increase -> more sea ice -> ice has high albedo compared to water -> less solar energy reflected, more absorbed if ice melts

Acceleration of the water cycle:

- Higher temp leads to more evaporation which leads to more water vapor in the atmosphere -> more condensation -> more precipitation - Evaporation increases everywhere, but precipitation mostly increases in areas where precipitation already occurs - Wet gets wetter and dry gets drier

Human impacts of climate change in CA:

- More extreme heat days - Ozone and particulate matter contribute ~8,800 deaths and $71b un healthcare costs annually - Northern CA: More winter precipitation; southern CA: mixed predictions/uncertain - Snowfall will be replaced by rain in the winter in CA=problem for infrastructure and water management

Basic operation of the water vapor feedback

- Positive feedback, acts globally - Begins with the warming of the atmosphere - Increase in temp leads to an increase in evaporation and then more water vapor in the atmosphere - With more evaporation and higher atmospheric temperature, we expect more water vapor in the atmosphere

Main reasons for the range of future climate predictions:

- There is a lot of variability in the land biosphere - Models differ: there are a lot of GCMs (so many different predications which vary based on how they are parameterized) - Lots of uncertainties - There is a range based on our own decisions and actions regarding the climate and climate policy going foreward - Many important climate processes cannot be resolved explicitly on the grid of a climate model (even the finer grid sized) - Processes need to be parameterized, leading to large differences between models - We don't know which parameterization is better than the others, so we need to consider the results from all models as equally likely. - Climate simulations are based on observed greenhouse gases and aerosols until 2000, followed by RCP scenario in 21st century

Main processes contributing to sea level rise, and their predicted future changes:

- Thermal Expansion o Caused by warming of the ocean (since water expands as it warms) o Molecules move faster when warmer o 1 degree C increase in temp= 0.5 rise of sea level - Melting Ice o Glaciers and ice sheets (land-based ice melting) o Greenland Ice Sheet Melting from above -> forms ponds +lakes -> creates a strong albedo feedback o Antarctica - West Antarctica ice shelf is greatest source of concern Melting from below - Predicted Future Changes o Protected sea level rise: With RCP 2.6: 0.3 TO 0.6 m With RCP 8.5: 0.5 to 1m • These estimates are very conservative and very uncertain The main reasons are from thermal expansion which is caused by warming of the ocean, and it makes molecules move faster. Then there is melting of ice, the melting forms strong albedo feedback. Positive warming feedback happens because the ocean is getting warmer and cannot hold as much CO2, making it warmer. The predicted future changes are the sea level rises with RCP 2.6 goes from 0.3 to 0.6m and with RCP 8.5 goes from 0.5 to 1m. - sea level rises could lead to flooding and destruction of infrastructure

Basic operation of carbon cycle feedbacks:

Carbon concentration feedback (CO2 fertilization)- (Negative feedback) more carbon in the atmosphere means there is more CO2 uptake by plants Carbon climate feedback- (Positive feedback) increasing temp -> increases the metabolism of soil microbes -> increases in decay of organic matter -> increase in CO2 in atmosphere - Overall, the two mechanisms combined create an overall negative feedback to climate change.

Climate change misconceptions framed in the context of paleoclimate (see group work 4):

Counterexamples to the misconceptions of climate change The climate has always changed, therefore it can't be because of something humans are doing: We know that anthropogenic CO2 is causing warming because the warming we have observed is not demonstrated on GCMs when human activities are not accounted for. Variations in atmospheric CO2 concentration in Earth's history have always followed those in temperature, therefore CO2 cannot be the reason for the rise in temperature happening now We know that the warming of the climate that is causing (and being caused by) positive warming feedbacks is due to human actions because these feedbacks were not present in pre-Industrial times. The temperature and CO2 climate feedback has always been occuring, but now humans are adding to it and intensifying it. It has always been the case that higher CO2 concentrations and higher temperatures went hand-in-hand--meaning that more CO2 = higher temperature = more CO2, and so on-- but now, humans are inserting CO2 into this cycle, intensifying the rise in temperature exponentially. The climate has always changed, therefore climate change can't be bad, or dangerous Yes, the climate has always changed, but the difference now is the rate of change, and the fact that we know the climate changing is the result of anthropogenic emissions (something humans are doing). The climate change that is happening now is extremely rapid and will lead to rising sea levels, extreme weather, and a change in how we must grow our food (because we are causing droughts and flooding, we will have to change our agricultural practices for mass producing food) Atmospheric CO2 concentration used to be much higher than it is now, and plant life thrived on Earth at that time While atmospheric CO2 has increased the amount of plant growth (greening), there will come a point when the plants can no longer grow, and they will become so water-stressed that they will die (browning).

Earth's energy budget, including transfer of heat in the atmosphere

Earth's energy budget is the various kinds and amounts of energy that enter and leave the Earth system. This is transferred through conduction (thermals), convection (heat rising, cool air sinking; this contributes to wind i.e. because of convection we have wind), and evaporation (latent heat)

Changes in the greenhouse effect due to human activities

Greenhouse effect: some incoming solar radiation passes through the atmosphere (visible range) and then is absorbed and re-emitted in all directions (IR Range) by Earth's surface. Some of this terrestrial radiation goes back up toward the atmosphere and interacts with the greenhouse gases in the atmosphere (absorbed/re-emitted in all directions, including back toward Earth's surface). Earth's surface is warmed more than it would be if greenhouse gases were not present. - Greenhouse effect is natural, but human activities like fossil fuel burning and deforestation are releasing more greenhouse gases into the atmosphere (ex. Carbon dioxide and methane), enhancing greenhouse effect and the overall global warming

Tropical circulation, including presence and absence of clouds

Hadley cells: there is one Hadley cell in each hemisphere (there is also a Ferrel cell and a polar cell) with westward and equatorward flow near the surface and eastward and poleward flow at higher altitudes; so it's an upwards sideways "circular" motion sorta) ICTZ band, produced by Hadley cells (a cloud "stripe" that is the main area where heat is rising and producing precipitation and clouds); The band of cloudiness associated with the rising branch of the Hadley cell Hadley cells- hot, wet air flows toward low pressure -> rises, expands, cools (high pressure) -> Flows towards low pressure (heat radiates to space)-> cool, dry air lowers -> subsides, condenses, warms -> warm, dry air -> trade winds picks up moisture and heat - A decrease in high clouds shrinks the patches that absorb terrestrial IR radiation, reducing the warming a negative climate feedback - A decrease in low clouds shrinks the patches of high albedo, leading to additional warming: a positive feedback

Interactions between the fast and slow carbon cycle (see group work 1):

Slow carbon cycle: long residence time and the fast carbon cycle: shorter residence time. Humans cause climate change by transferring carbon from the slow to the fast carbon cycle. Fluxes exchange carbon between pools (plant biomass, atmosphere, surface ocean, etc.) Carbon makes it from the slow carbon cycle into the fast carbon cycle by: Human (anthropogenic) emissions Burning fossil fuels Carbon makes it from the fast carbon cycle into the slow carbon cycle by: Formation of fossil fuels

Solar vs terrestrial radiation, interaction with atmospheric gases

Solar Radiation- radiation from the sun enters at the top of the atmosphere. Arrives from the sun at the top of the atmosphere and has shorter wavelengths (more damaging radiation). Not absorbed strongly in the atmosphere (with one exception), so sunlight tends to get through the ground Terrestrial Radiation- radiation also comes from the earth's surface and atmosphere. It also has longer wavelengths (less energetic radiation). It is both absorbed and emitted into the atmosphere. Such a big player in the greenhouse effect that small changes can alter the surface temp of a planet - Large fraction of the sun's radiation makes it to the sun's surface because the atmosphere is relatively transparent to the wavelengths of solar radiation Water vapor and carbon dioxide both interact with terrestrial radiation (greenhouse gases)

Zero emissions, negative emissions:

The severity of climate change/warming is determined by the cumulative carbon emissions; to achieve any of the lower RCPs, we will need zero emissions soon (expected warming is based on how much carbon we are emitting; this makes sense because carbon dioxide is a greenhouse gas) - To stay below 2˙C warming, we need to achieve dramatic emissions reductions and probably even negative emissions technologies Negative Emissions Technologies- - (a type of geoengineering, large-scale climate change with other types of human interference) - Carbon Capture and Storage (CSS): the process by which CO2 is isolated from the emission gas stream, compressed, and transported to an injection site where it is permanently stored underground o But it costs more energy to do this, so the power plant becomes less efficient o Risky bc of leaks - Injecting aerosols into the stratosphere to increase albedo: injection of sulfate particles into the stratosphere to achieve artificial reflection of sunlight o This has potentially severe side effects, like shifts in precipitation zones, surface drying, and milky skies - Cloud albedo enhancement: seeding clouds with aerosols to enhance the number of water droplets in clouds, hence increasing the clouds' albedo But stratospheric aerosol solar radiation engineering is expensive, cannot be deployed quickly, would need to be applied continuously and indefinitely, and does nothing to address ocean acidification

Attributing and predicting climate change:

We use climate models to demonstrate that changes in the climate system can be attributed to our own carbon emissions. • Global Climate Models (GCMs)-- there are about 30 from different research which we intercompare • Small-scale processes, like clouds, precipitation, and hurricanes, need to be parameterized; this leads to large differences between models Coupled Model Intercomparison Project (CIMP5) is an average of different GCMs, used as an average to compare and analyze observed changes • We know that humans are causing some of the warming that is occurring because when human activities are left out of the models, the models do not replicate the warming we have observed. We can still observe fluctuations without human activity, though, due to things like sun spots, volcano activity, and El Niño - We can use climate models to demonstrate that changes in the climate system can be attributed to our own carbon emissions - We observe a lot of changes in our climate system Predictions- GCM (general circulation Model) there are about 30 GCM's from different research teams around the world, model intercomparison is a major activity. Includes lots of climate processes - When human activities are left out, the models fail to simulate the observed increase in temperature - When the radiative forcing due to human activities included in climate simulations, the observed temperature trend over the 20th century is reproduced - GCMs predict the climate response over time starting from the current state of the climate and adding the future radiative forcing from human activities based on different scenarios (RCPs) RCP: Representative Concentration Pathway: 4 trajectories of greenhouse gas concentrations used for climate modelling. The RCPs are 8.5, 6, 4.5, and 2.6. • 2.6, the RCP with the lowest greenhouse gas concentration prediction, is likely no longer achievable. We base climate simulations on observed greenhouse gas concentrations and aerosols until the year 2000, followed by the RCP scenario in the 21st century.

Difference between weather and climate

Weather- Short-term evolution of the atmosphere (few days) Climate- Long-term statistics of weather (30 years) - Climate is what you expect, weather is what you get Climate Components- Atmosphere, vegetation, land surface, ice, and ocean

Climate sensitivity:

equilibrium climate sensitivity: refers to the sensitivity of the climate system to radiative forcing after it has fully adjusted in response to CO2 doubling. transient climate sensitivity: refers to the sensitivity of the climate system to radiative forcing while it responds to a change in radiative forcing; specifically refers to the state of the climate system at the time of CO2 doubling Warming continues for centuries after CO2 levels have stabilized because the ocean acts a huge buffer that