Presentation on theme: "Climate Change and its Effects on the Global Ocean Nicole Del Monaco."— Presentation transcript:
Climate Change and its Effects on the Global Ocean Nicole Del Monaco
Physical Processes and Feedback: Overview The key issue with climate change to be addressed is the response to the changes in forcing i.e. concern on large-scale global circulation in the atmosphere and ocean. This forcing determines overall climate sensitivity Within atmospheric and oceanic circulation, there are many coupled, comprehensive, large-scale dynamical feedbacks These large-scale dynamical feedbacks are coupled with small scale processes within the climate system The various feedbacks in the climate system may amplify (positive feedbacks) or diminish (negative feedbacks) the original response Take home point: Forcings, feedbacks and the dynamics of the climate system determine how much and how fast the climate changes.
Atmospheric Processes and Feedbacks: Water Vapor Feedback Generally, Earths radiation balance is closely achieved since the Outgoing Longwave Radiation (OLR) equals the Shortwave Absorbed Radiation (SAR) received at high energy from the sun An increase in the amount of greenhouse gases contained in Earths atmosphere would reduce the emission of OLR. To compensate, the climate achieves a new equilibrium by warming until the OLR increases enough to balance the SAR Enhanced warming of the atmosphere enhanced evaporation more water vapor further warming further evaporation ever more water vapor Water vapor is a very powerful greenhouse gas. As water vapor increases as the climate warms, the additional reduction of OLR requires a new equilibrium to be met. Referred to as a positive feedback loop
Atmospheric Processes and Feedbacks: Ice-Albedo Feedback Ice has a high albedo. As ice expands, more solar radiation is reflected to space, less is absorbed by the surface, and temperatures decrease. Cooler temperatures more ice growth more reflection of solar radiation back to space even cooler temperatures Positive feedback loop However, can also have opposite effect (similar to cloud feedback) – damped feedback Ice melts solar radiation will be absorbed by surface raises temperature more ice melts This feedback may act more quickly over oceans then land because sea ice melts faster than large continental sheets
Atmospheric Processes and Feedbacks: Cloud Feedback Clouds are formed by condensed water vapor. They therefore become a problem because they effect OLR in the same way that water vapor does, increasing the temperature of the atmosphere. However, clouds also reflect incoming solar radiation because of its high albedo. Clouds have a warming and cooling effect However, recent research suggests that cloud feedback is generally warming There was hesitance because of cloud changes near the equator, tropics, and subtropics. Data and research conducted suggested that warming is occurring in all of these regions To further prove that clouds have a generally positive feedback:
Cloud Feedback Figure 4A and 4B represent climate shifts between the years , while figures 2C and 2D represent climate shifts of Figure 4 Figure 3 Figure 3 represents data for a typical El Nino event Figure 5 Enhanced upper-level cloud cover is consistent with the weakening of subsidence over the NE Pacific.
Feedback Loops Only a fairly small fraction (40 W/m 2 or 10.3%) of the 390 W/m 2 of infrared radiation emitted from Earth's surface makes it directly into space without first being trapped by various greenhouse gases in the atmosphere. In other words, about 89.7% of the outgoing infrared radiation is affected by the greenhouse effect. Water vapor "intercepts" about 32% to 59% (36% to 66% times 89.7%) of the outgoing infrared. Clouds "intercept" about 17% to 27% (19% to 30% times 89.7%) of the outgoing infrared. Water vapor plus cloud droplets combine to "intercept" about 59% to 76% (66% to 85% times 89.7%) of the outgoing longwave radiation. The bottom line? Water vapor and clouds already play a huge role in producing the greenhouse effect, and thereby influencing Earth's climate. Figure 7
Oceanic Processes and Feedbacks: Thermohaline Circulation Figure 8
Oceanic Processes and Feedbacks: Thermohaline Circulation A special concern are possible reductions of the Atlantic THC caused by warming and freshening of high latitude surface water associated with global warming Increased air moisture, heat, and precipitation in pole regions and the resulting increase in river discharge into the Arctic Ocean can lower salinity and cause warmer surface temperatures, as well as create weaker water circulation in the Atlantic Ocean. This overall contributes to the reduction of water density in the formation regions of NADW Damped feedback: low latitude advection increased sea surface temperature reduction in the Atlantic THC Self-reinforced feedback: low latitude advection increased evaporation increased sea surface salinity normal Atlantic THC (sinking at poles) Figure 9
No such deep overturning occurs in the North Pacific, where surface waters are too fresh to sink. Strong cooling also occurs in the Bering Sea in the North Pacific, but the lack of a meridional land barrier (i.e. MidAtlantic Ridge) in the Southern Ocean prevents the existence of strong east–west pressure gradients needed to balance a southward geostrophic surface flow Oceanic Processes and Feedbacks: Thermohaline Circulation
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