GHY section 4
Aerosol optical depth (AOD)
Variable used by scientists to describe the amount of solar radiation scattered or absorbed by aerosols (instrument: sun photometer)
Effects on ecosystems
Carbon Fertilization: Depends on whether they are C3 or C4 Plants. -Corn is at a disadvantage compared to C3 weeds in a world with higher CO2 because C4 plants do not photosynthesize as well Changes of speciations within forests -Fate of the spruce-fir ecosystem in S. Apps? Rising biosphere in mountains Marine Ecosystems Coral Reefs
Earth's Surface Properties and Climate Change- Snow and Ice Cover
Changes in mean regional snow cover may contribute to climate variability and climate change. - Fresh-fallen snow typically reflects 80% or more of incident solar radiation, reducing the amount of solar heating and lowering the daily maximum air temperature. Whereas changes in regional snow cover might impact climate variability over the short-term, changes in Earth's sea ice or glacial ice coverage are likely to have longer-lasting effects on climate. Ice reflects much more incident solar radiation than either the ocean or snow-free land. -Any change in glacial or sea ice cover would affect climate.
(ESPaCC) Sea-Surface Temperature Pattern
Changes in ocean circulation and sea-surface temperatures contribute to large-scale climate change and climate variability. -Some climate shifts can be abrupt, occurring in a decade or less.
Sunspots
Changes in solar energy output apparently are related to sunspot number. More sunspots may contribute to a warmer global climate and fewer sunspots may translate into a colder global climate. Typically lasts only a few days. Number of sunspots varies systematically with time between successive sunspot maxima or minima (averaging about 11 years).
CAN-DOO
Climate Action Network through Direct Observations and Outreach
Trends in Greenhouse Gases
-Most of the increase in globally-averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG (greenhouse gas) concentrations -Fossil fuel combustion accounts for 75% of the increase in atmospheric carbon dioxide --deforestation is likely responsible for the balance -Rising levels of other infrared-absorbing gases associated with human activity (e.g. methane, nitrous oxide, halocarbons, and ozone) enhance the greenhouse effect
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Global temperature projections
Global temperatures are projected to increase by 1.8 to 4.0 degrees C by 2100 Warming is projected to be most pronounced at higher latitudes of the Northern Hemisphere, especially north of 60 degreesN Greatest warming likely to occur over land Little difference in projected warming among different emission scenarios for the next 25 years
Changes in land use and land cover (due to human activity)
Human development has transformed an estimated one-third to one-half of Earth's land surfaces -Changes can affect the vertical flux of heat and moisture --influences where and when thunderstorms occur --may modify atmospheric and oceanic circulation -At middle latitudes, clearing of forests for agriculture and reforestation of abandoned farm land has caused regional climate change
Human Activity and Climate Change
In 2013, the Intergovernmental Panel on Climate Change concluded that global warming since the mid-20th century very likely (estimated probability greater than 90%) was caused mostly (>50%) by human activities
Volcanoes and Climate Change
In violent eruptions, volcanoes discharge ash particles and sulfur dioxide into the stratosphere, creating a veil that can cause cooling at Earth's surface. -Must be a violent eruption, at low latitudes and rich in SO2. By influencing the flux of radiation and attendant changes in global circulation patterns, the Pinatubo eruption was likely responsible for the cool summer of 19992 over continental areas of the Northern Hemisphere. An eruption is unlikely to lower the mean hemispheric or global surface temperature by more than about 1.0 Celsius degree (for a year or two) although the magnitude of local and regional temperature change may be greater.
Radiative forcing of land cover change
Land cover change since 1850 has generally led to higher surface albedo and a slight negative radiative forcing. -best estimate is -0.24 w m^-2 However, spatial variability is quite high, with some areas showing no change in RF and other areas more negative than -5 w m^-2. With tropical deforestation becoming more significant in recent decades, warming due to reduced evaporation may become more significant globally than increased albedo.
Atmospheric Composition and Climate Change
Natural processes have played important roles in regulating levels of greenhouse gases and global climate. -Extinctions of plants and animals have been linked to increases in atmospheric CO2 levels associated with massive volcanic eruptions. -Methane was an important contributor to post-glacial warming at high latitudes. -- Release from methane hydrates on the seafloor -- Emission from northern wetlands as temperatures rose -- Thermokarst lakes
Attribution Skeptics
No anthropogenic forcing on climate change
Trend Skeptics
No upward trend in temperatures
Limitations of GCMs
A model is a hypothesis about how the climate system operates! Only the dynamic core of the models represent basic physics. All other components of these models are parameterizations, which means they are not fundamental physics but engineering code with tunable parameters. *It is very difficult to accurately parameterize clouds and cloud microphysical processes in weather or climate models!
IPCC AR4 Carbon Emission Scenarios
A2- More divided world (high emissions) -a more divided world with independently operating and self-reliant nations, continuously increasing population, regionally oriented economic development, slower and more fragmented technological changes A1B- More integrated world (high emissions) -a more integrated world with rapid economic growth, global population reaching 9 billion in 2050, and convergence of income and way of life, balanced emphasis on all energy sources B1- Ecologically friendly world (moderate emissions) -a more integrated world and more ecologically friendly, reductions in materialism and the introduction of clear and resource efficient technologies
Why are Greenhouse Gases Important?
Absorb long-wave terrestrial radiation, heating the atmosphere, and radiating this energy back to the surface. Critical for life on Earth. Without it, surface temps would be very cold at night. Too much of a good thing, however, is a concern.
Changes in Surface Albedo
Anthropogenic changes to the physical properties of the land surface can perturb the climate. -Directly exerting a radiative forcing -Modifying other processes such as latent and sensible heat fluxes (^We're now talking about the water cycle: precipitation, amount of water in atmosphere in certain regions, etc. which are altered when we modify land cover) Large-scale character of vegetation can affect surface albedo. -Albedo of agricultural land can be very different from that of a natural landscape, especially forest -Particular important when snow is present, as open land can be highly reflective with snow cover, while a forest is not
Global Radiative Equilibrium and Climate Change
Any Change in either energy input or energy output will shift the Earth-atmosphere-land-ocean system to a new equilibrium and change the planet's climate.
Factors affecting future carbon emissions
As long as fossil fuels remain reasonably abundant, future carbon emissions can be approximated by three factors: -Human populations -Change in emissions per person -Changes in efficiency of carbon use Increase in carbon emissions = increase in population x change in emissions per persons changes in efficiency of carbon use
Summary of climate projections
Sea ice, particularly in the arctic during July, August, and September, will continue to decline dramatically. Warm-phase of ENSO (El Nino) may become more frequent. Frequency of heat waves is likely to increase. Length of growing season is likely to increase in mid-latitudes with a corresponding decrease in the number of frost days. Continued ablation of the Greenland Icecap is likely, with a volume reduction of 20% by 2275 AD.
Adapting to climate change
Sea level rise: Approximately 10% of worlds population is found within Low Elevation Coastal Zones (LECZs) -60% of population of the Netherlands lives within LECZs -significant problem facing society Water management: How to ensure adequate and clean water when quantity and dependability of existing supplies is decreasing? -Glacier retreat in tropical Andes
Atlantic Meridional Overturning Circulation
Best-documented type of abrupt climate change in paleoclimatic archives is associated with changes in ocean circulation, especially in the North Atlantic. Also referred to as "Thermohaline Circulation".
Atmospheric aerosols
Solid or liquide particles suspended in the air -Can influence weather and climate by directly and indirectly affecting the amount of solar radiation reaching the earth's surface, which can lead to warming and cooling in different regions of the world. *Overall RF is negative, however.*
Solar Variability and Climate Change
Sun's total energy output at all wavelengths is not constant. Numerical global climate models predict that only a 1% change in the sun's energy output could significantly alter the mean temperature of the Earth-atmosphere-land-ocean system
Maunder Minimum and The Little Ice Age
Sunspot activity greatly diminished during the 70-year period from 1645 to 1715 and coincided with a cold episode in Europe. The magnitude of the variation in solar energy output during an 11-year solar cycle is so little that some amplification mechanism is required for sunspots to influence climate.
Impact Skeptics
Science is overstated for future impacts
Human Activity and Climate Change: Aerosols
*90% of anthropogenic aerosols are byproducts of fossil fuel burning in the Northern Hemisphere.* -Cause either cooling (*sulfurous aerosols*) or warming (*black carbon*) of the atmosphere Aerosols can alter the number, mean size, and size distribution of cloud droplets. *The direct radiative forcing of aerosols is estimated to offset the CO2 warming by almost one-third.*
What is Radiative Forcing?
*The Change in net (down minus up) irradiance (solar plus long wave; in Wm^-2) at the tropopause* Abbreviated RF Positive RF implies warming Negative RF implies cooling
Changes in land cover since 1750
Cropland area expanded from 1750 to 1950 across Europe, Gangetic Plain, and in North America. Since that time, croplands have been abandoned in Europe, North America and China, with an increase in forested areas. Deforestation is occurring quite rapidly in the tropics. Forests turned to grass leads to higher albedo which results in negative radiative forcing (cooling).
Human Impacts
Floods, droughts, and climate extremes likely to increase. Global conflicts may be exacerbated? -Arctic claims in response to decreasing summer sea ice? -Environmental refugees Food shortages and higher food prices?
Factors that can alter the global radiative equilibrium
Fluctuations in solar energy output Changes in Earth's orbit about the sun Volcanic eruptions Variations in atmospheric chemistry Alterations in Earth's surface properties Certain human activities
Anthropogenic Forcings on Climate
Greenhouse gases Aerosols Land use/land cover change
What is surface albedo and who is it important in the context of climate change?
High albedo- more reflected back Low albedo- more absorbed Alters the surface energy balance How have humans changed surface albedo?
Mitigation strategies
Kyoto protocol -CO2 emissions 5% below 1990 -Ratified by 182 countries, bi-partisan rejection in U.S. Energy conservation and other "Soft" Measures Alternative energy sources -Wind, nuclear, solar, tidal, biomass-based fuels Carbon capture and storage (CSS) -Also known as carbon sequestration and involves burying carbon in ground Geoengineering of global climate
General Circulation Models
Mathematical representations of the climate system, expressed as computer codes and run on powerful computers. Operate in 3-D and have capacity to represent spatial distribution of land, water, ice, elevation of mountains, vertical distribution of greenhouse gases, and changes in solar radiation. Operation of GCMs incorporates physical laws and equations that govern the circulation of Earth's atmosphere.
(ESPaCC) Shrinkage of Arctic Sea-Ice Cover
Melting of floating sea ice does not raise sea level, but it can alter climate significantly. Shrinkage of Arctic sea ice is likely to trigger an ice-albedo feedback mechanism that would accelerate melting of sea ice and amplify warming. Arctic sea ice cover varies seasonally and exhibits some long term trends. In recent years there has been a decline in the winter maximum extent of ice. *After 2000, the rate of reduction of Arctic sea ice cover accelerated. The end-of-summer ice extent reached a record low in 2007. If current trends continue, by 2037 the Arctic Ocean may be free of sea ice in the summer.*
How reliable are GCMs?
One source of confidence comes from the fact that model fundamentals are based on established physical laws... Second source of confidence comes from the ability of models to stimulate (more or less) important aspects of the current climate.
Anthropogenic aerosols
Particles from the burning of fossil fuels and biomass, smoke, and agricultural dust
Naturallly occurring aerosols
Particles from trees, sea salt, dust, and volcanic dust
Global precipitation projections
Precipitation is projected to increase in the tropics and decrease in the sub-tropics, and increase in the middle latitudes and polar regions. Precipitation intensity is also projected to increase in most regions of the world. The number of dry days is projected to increase in much of the tropics, sub-tropics, and middle latitudes.
Black carbon on snow
Presence of soot particles in snow causes a decrease of albedo and can affect snowmelt -best estimate of RF is +0.10 w m^-2
What forcing mechanisms can bring about climate change and climate variability over a broad range of time and spatial scales?
The complex spectrum of climate variability and climate change is a response to the interactions of many forcing agents and mechanisms operating both internally and externally relative to the Earth-atmosphere-land-ocean system. One way to organize our thinking on the many possible causes of climate change is to match a possible cause with a specific climate fluctuation based on similar periods
KNOW DIRECT AND INDIRECT EFFECTS OF AEROSOLS DIAGRAM
in powerpoint 34? CDNC- Cloud droplet number concentration LWC- Liquid water content Be familiar with direct effects and indirect effects