Climate change caused by anthropogenic CO2 emissions persists for over a thousand years and even short lived gases such as methane have long-term effects once they warm the deep ocean.
Carbon dioxide displays exceptional persistence that renders its warming nearly irreversible for more than 1,000 years..(edit).. dampening factors that slow temperature increase during periods of increasing concentration also slow the loss of energy from the Earth’s climate system if radiative forcing is reduced.
One thousand years after CO2 emissions stop 70% of the warming persists.
Fig. 4. Relative changes in radiative forcing (Upper) and warming (Lower) in the Bern 2.5CC model, for the same assumed profile of increasing radiative forcing over 100 y, followed by a stop of emissions as in Fig. 3, for a range of greenhouse gases of varying lifetimes. The gases considered are HFC-152a (1.4-y lifetime), methane (≈10-y lifetime), N2O (114-y lifetime), carbon dioxide (see text), and CF4 (50,000-y lifetime). All quantities are normalized to one when emissions stop, in order to examine relative changes.
Dr. Susan Solomon and her co-investigators report that these results are based on an ocean atmosphere model that fully accounts for radiation physics but does not include changes in the earth's uptake of heat due to ice melting and vegetation changes. Thus the model significantly underestimates the irreversibility of the climate system.
It should be noted that, although the Bern 2.5CC EMIC includes a representation of the surface and deep ocean, it does not include processes such as ice sheet losses or changes in the Earth’s albedo linked to evolution of vegetation.
The analysis by Dr. Solomon goes into detail on the persistence of warming caused by significant greenhouse gases. To this point in time, about 1/3 of the historical heating caused by greenhouse gases has been retained by the oceans and 2/3 has been radiated back to space. The slow thermal response of the ocean has moderated the rate of increase of global temperatures. However, once warmed, the ocean delays return to once normal temperatures. According to Dr Solomon:
energy that is added to the ocean remains available to be transferred back to the atmosphere for centuries after cessation of emissions.
The heat content of the upper ocean has been rising rapidly since 1995.
Deep water is also warming due to the sinking of warmer than normal water around Antarctica. Deep water warming is contributing to sea level rise. The warming of deep water will affect global temperatures for hundreds, possibly thousands, of years.
"Previous studies have shown that the upper ocean is warming, but our analysis determines how much additional heat the deep ocean is storing from warming observed all the way to the ocean floor," said Sarah Purkey, an oceanographer at the University of Washington and lead author of the study.
This study shows that the deep ocean – below about 3,300 feet – is taking up about 16 percent of what the upper ocean is absorbing. The authors note that there are several possible causes for this deep warming: a shift in Southern Ocean winds, a change in the density of what is called Antarctic Bottom Water, or how quickly that bottom water is formed near the Antarctic, where it sinks to fill the deepest, coldest portions of the ocean around much of the globe.
These two reports published this year show that ocean warming is a near and present danger. Dr. Solomon's study addresses an urgent problem. Her conclusion stresses the need for immediate action.
The analysis provided here is intended in part as an aid to communication on this important science/policy point. The persistence of the warming perturbation due to various gases can be described as a reflection of how the time history of radiative forcing interacts with ocean heat uptake. Maintaining a forcing for a longer period of time transfers more heat to the deep relative to the shallow ocean, with a correspondingly longer timescale for release of energy if emissions were to be halted (17), so that the net effect on climate change depends upon both ocean physics and how long the gas is retained in the atmosphere.
Carbon dioxide and perfluorocarbons represent special cases, primarily because zero emissions do not lead to zero concentrations for thousands of years. Nonlinear optical depth effects are also significant (ed note: to persistence of warming) for carbon dioxide and methane.
We have shown how ocean heat transport and its response to climate change is crucial to evaluation of the speed with which near-term warming would abate if emissions of various gases were to be reduced, including methane, nitrous oxide, and various hydrofluorocarbons; the same considerations apply to absorbing aerosols including black carbon. This study has explained why the slow timescales of the ocean imply that actions to mitigate the climate impacts of these warming agents would be most effective if undertaken sooner; conversely such actions would become less effective the longer the radiative forcing is maintained.
Ocean-atmosphere models predict that climate change and warming oceans will redistribute water vapor and precipitation globally. Recent studies show that these model forecasts may be already verifying.
Soils over large areas of the southern hemisphere are drying up. Since 1998 evaporation and plant transpiration has increased over the southern hemisphere.
"We didn't expect to see this shift in evapotranspiration over such a large area of the Southern Hemisphere," said study co-author Beverly Law, a professor of global change forest science at Oregon State University. "It is critical to continue such long-term observations, because until we monitor this for a longer period of time, we can't be sure why this is occurring."
Some of the areas with the most severe drying include southeast Africa, much of Australia, central India, large parts of South America, and some of Indonesia. Most of these regions are historically dry, but some are actually tropical rain forests
This is precisely what a model study published this week in Geophysical Research letters predicts. The monsoons in south Asia will strengthen, bringing heavier rains and floods to south Asia and Africa, while the southern hemisphere will dry out, according to model and paleoclimate studies.
This study calibrated a climate model against known climate changes from 6000 years before present to today. The Asian-African monsoon was stronger and wetter 6000 years ago while the western U.S. was drier. The figure 3e on the bottom left shows that anthropogenic greenhouse gas global warming will cause a strengthening of the Asian monsoon similar to the strengthening that was caused by orbital variations 6000 years ago.
Figure 3. Changes of atmospheric moisture budget components averaged over the Northern Hemisphere: (a, b) water vapor influx, (c, d) evaporation and (e, f) precipitation during boreal summer (Figures 3a, 3c, and 3e) and winter (Figures 3b, 3d, and 3f) versus the changes in surface air temperature according to simulations of KCM forced by orbital variations (red dots) and GHG emission (black dots), correspondingly. Negative values of water vapor advection depict the export of water vapor to the Southern Hemisphere.
A warming climate strengthens the subtropical high pressure areas in the southern hemisphere and the northern Pacific Ocean. The stronger high in the south Indian ocean transports moisture north into south Asia.
Thus the catastrophic flooding in south Asia this summer is consistent with model predictions of the effects of climate change. Likewise, the drying of much of the southern hemisphere and the U.S southwest is consistent with paleoclimatology and model predictions.
Figure 1. Annual mean precipitation (mm/day) according to (a) CMAP observations and (b) KCM simulations for the period 1979–2008. Reconstructions of (c) lake level changes for 6 kyr BP in comparison to (d) changes in simulated precipitation minus evaporation (mm/day). Yellow and blue areas (Figure 1c) show drier and wetter conditions during mid-Holocene (compared to preindustrial), respectively. The model estimates (Figure 1d) are significant at the 10% level of the t-test.
The authors conclude that climate change is changing the hydrologic cycle.
According to our results, surface warming induced either by a positive northern hemisphere summer insolation anomaly (orbital) or by GHG forcing leads to a higher seasonal amplitude of the cross-equatorial water vapor exchange with stronger changes induced by the orbital parameters. The higher moisture and precipitation in summer can be fully attributed to the advection from the Southern Hemisphere, while evaporation remains largely unaffected. This effect is sufficiently strong to dominate the annual mean signal, such that the resulting precipitation increase in the Northern Hemisphere is offset by decreasing precipitation in the Southern Hemisphere. In contrast in the GHG scenario, the Northern Hemisphere moisture and precipitation increase during summer is caused equally by advection and evaporation. As a result of the stronger seasonal variations of cross-equatorial water vapor transport, the rate of change of the Northern Hemisphere precipitable water varies between 9.2% K−1 in summer and 5.0% K−1 in winter in the paleo simulations.
[16] Our results have implications for the hydrological cycle in a warmer future climate, where on millennial time scales both effects (GHG and increasing Northern Hemisphere summer insolation) are expected to combine.
The likely consequences of this change in the hydrologic cycle is drought in the Amazon, southern Africa, Australia, western Russia and the western United States and increased flooding by the Asian and African monsoons.
This summer's "freak" weather may be a portent of future climate.
Unless, we rapidly cut emissions the changes will be permanent.
UPDATE
California: Vote no on 23 and from RL Miller
Proposition 25 will end budget gridlock by requiring a simple majority, rather than a 2/3 vote, to pass a state budget; both the California Democratic Party and the Los Angeles Times recommend a "yes" vote. Proposition 26 seeks to require a 2/3 majority on certain business fees by declaring them "taxes"; both the California Democratic Party and Los Angeles Times recommend "no" votes.
While officially remaining neutral on Proposition 23, California-based oil companies Chevron and Occidental, and the California Chamber of Commerce, have been quietly funnelling their cash into a No on 25/Yes on 26 political action committee.