This guest post comes from scientist FishOutOfWater.
The north Atlantic ocean is heating faster than all the world’s oceans because of the increased flow from the Indian ocean to the Atlantic ocean.The rapidly strengthening greenhouse effect produced by exponentially increasing human emissions of greenhouse gases is affecting earth’s climate unevenly. The North Atlantic ocean is heating the fastest of the world’s oceans. The rapidly increasing heat content of the north Atlantic ocean is fueling the rapid increase in weather related disasters in the United States. This increase in disasters is not a cyclic phenomenon. Because the north Atlantic is at the end of the great “conveyor belt” of the global circulation of salt and heat - the thermohaline circulation - it accumulates heat the fastest of the oceans when the earth is heating up. Since 1995, the north Atlantic has been heating at a record rate.
Gulf Stream loop ahead of Hurricane Sandy, Oct. 25 sensed by very high resolution radiometry. Sandy’s record low pressure was fueled by record oceanic heat content.
Likewise, because of its deep connection to the Arctic ocean, the North Atlantic cools the fastest when the earth cools. In fact, the north Atlantic and Arctic oceans are treated as a single entity by some models. The extreme sensitivity of the Arctic ocean and the north Atlantic to slight changes in the earth’s radiation balance make the north Atlantic, north America and western Europe very sensitive to changes in global average temperature. That is why minor orbital variations brought continental glaciers to north America and Europe. Minor changes in radiation balance were amplified by increasing amounts of snow and ice. This quirk of climate and geography makes the United States is the global hypocenter of climate change.
Superstorm Sandy has awakened NBC into asking the right questions to the right experts. This 2 minute clip gets the basics of the connections of climate change to extreme weather right.
Hurricane Sandy 3:40pm EDT Oct 27. Sandy can be seen interacting with a cold front running from the Florida panhandle to Lake Ontario. Sandy was a hybrid tropical/frontal storm at this time, maintaining its strength despite very strong wind shear.
Global Warming made Hurricane Sandy’s regional record low pressure possible.
The strength of a hurricane is, in part, a function of the thermodynamics driving it. A hurricane is a heat engine. MIT Professor Kerry Emanuel has published on the physics of hurricanes. He has developed a numerical method for calculating the potential minimum pressure and maximum winds for a hurricane based on the sea surface temperature and the thermodynamic profiles of the atmosphere taken from NOAA’s GFS MRF model. On Monday October, 22, when Sandy became a named storm his model showed the potential for a 940mb low on the north wall of the Gulf stream north-east of Cape Hatteras. If the water temperature had not been much above normal, the potential energy would not have been available to develop the record low pressures observed in Sandy. Because Sandy was a hybrid storm the physics becomes even more complicated but high oceanic heat content was the energy source that drove Sandy to record low pressures for this part of the Atlantic.
Large intense storms such as Sandy stir the oceans down to 100 meters or more and upwell water from depth. They require an extraordinarily large volume of warm water to maintain their strength. Sandy tracked over water that had both high sea surface temperatures and high temperatures at 100 meters depth. The heat content of water on the east coast this October has been greater than the October heat content of the record Atlantic storm year of 2005. In fact, the heat content of the western north Atlantic has been rising for decades and is at record high levels.
26 Celsius isotherm depth on Oct. 25, 2005
26 Celsius isotherm depth on Oct. 25, 2012
The greatest increase in oceanic heat content on earth is in the north Atlantic off of the coast of the northeastern U.S. and the Canadian maritime provinces. Levitus et al, 2012
The north wall of the Gulf Stream has been moving north for decades. The Gulf stream is the warm surface current of the front between the Atlantic warm pool and cold polar water. This front extends to a depth of greater than 1000 meters. An enormous amount of heat is involved in moving it north. A significant fraction of the heating of the earth has gone into expanding the Atlantic warm pool. The northward expansion of the Atlantic warm pool has fueled the increasing destructive power of storms affecting the northeastern U.S. and eastern Canada.
Global Ocean Heat Content Trends Since 1955, Levitus et al, 2012
If it seems like extreme storms are increasing over the Northeast USA, then you are right. The climate extremes index by the NOAA NCDC agrees.
The big jump in the extreme weather index in the northeast happened after north Atlantic waters began to warm rapidly in the late ’90’s. Moreover, Atlantic hurricane numbers and intensity show the same increasing trend with increasing sea surface temperature.
Mann and Emanuel showed the direct correlation between north Atlantic sea surface temperatures and the number of hurricanes.
The earth has been heating rapidly since 1990. Most of the heat is stored in the oceans.
The stored heat has been concentrated in the subtropical warm pools of the ocean basins. The warm pools have expanded poleward and become saltier while tropical convection has strengthened. Water rich areas have become wetter, water poor areas have become drier and storms have intensified. The global water cycle has strengthened.
Large, robust, and spatially coherent multidecadal linear trends in salinity to 2000-dbar depth are found. Salinity increases at the sea surface are found in evaporation-dominated regions and freshening in precipitation dominated regions, with the spatial pattern of change strongly resembling that of the mean salinity field, consistent with an amplification of the global hydrological cycle.
The expansion of the warm pool in the south Indian Ocean has had a profound effect on the distribution of global heat and climate change. The poleward expansion of this warm pool has increased the rate of flow of water from the Indian Ocean to the south Atlantic ocean because the effective width of the passage south of capes of South Africa has increased. The intensified trade winds across the worlds oceans and the wider passage for the Agulhas leakage around South Africa has increased the flux of water moving towards the north Atlantic.
Movie for Van Sebille et al. (2011, J. Phys. Oceanogr.) showing the locations of 10,000 super-trajectories as a function of time. The super-trajectories are constructed from data from observational drifting buoys in the real ocean. All super-trajectories shown here start in the Agulhas Current and end either at the Greenland-Scotland Ridge or in the Labrador Sea within 100 years.
Increased flow from the Indian ocean to the Atlantic ocean is increasing the warming rate of the North Atlantic. This redistribution of heat is changing global weather patterns.
As the upper layer of the world ocean warms gradually during the 20th century, the inter?ocean heat transport from the Indian to Atlantic basin should be enhanced, and the Atlantic Ocean should therefore gain extra heat due to the increased upper ocean temperature of the inflow via the Agulhas leakage.
Consistent with this hypothesis, instrumental records indicate that the Atlantic Ocean has warmed substantially more than any other ocean basin since the mid?20th century.
A surface?forced global ocean?ice coupled model is used to test this hypothesis and to find that the observed warming trend of the Atlantic Ocean since the 1950s is largely due to an increase in the inter?ocean heat transport from the Indian Ocean. Further analysis reveals that the increased inter?ocean heat transport is not only caused by the increased upper ocean temperature of the inflow but also, and more strongly, by the increased Agulhas Current leakage, which is augmented by the strengthening of the wind stress curl over the South Atlantic and Indian subtropical gyre.
The strengthened subtropical high pressure areas and trade winds in the Pacific Ocean have strengthened the cool currents running along the west coasts of North America and South America. This has cooled the waters off the California coast, reducing winter season rainfall to California and the southwest. The polar jet stream - the storm track - along the west coast has moved north in response to the stronger Pacific high.
Natural phases of warm and cool waters have been observed along the Pacific Coast. The cool phase is associated with southwestern U.S. drought.
Archaeological and paleoclimatological evidence shows that southwester megadroughts happened in the past when the Pacific oscillation stuck in the cool phase. In the medieval warming period, the Pacific coast was stuck in a persistent cool phase and the southwest had recurrent long periods of drought. Mesa Verde and other large habitations in the southwest were abandoned because of drought and conflict.
The pattern of a cold Pacific coast and a warm Atlantic coast has severe consequences for U.S. weather. This pattern brings drought to the southwest and west. These droughts frequently extend to the plains and the southern states with severe effects on food production in the grain belt. It increases the intensity of storms in the northeast and brings more hurricanes to the Atlantic basin. The warm Atlantic / cool Pacific pattern is a recipe for disaster. It is the pattern we have been in for the past decade.
This paper by U.S.Geological Survey scientists published in 2004 in the Proceedings of the National Academy of Science warned of dust-bowl like droughts that this pattern would cause. The extreme droughts in Texas, Mexico and the midcontinent over the past 3 years proved their warnings prescient.
Recent droughts with broad impacts over the conterminous U.S. (1996, 1999–2002) were associated with North Atlantic warming (positive AMO) and northeastern and tropical Pacific cooling (negative PDO). Much of the long-term predictability of drought frequency may reside in the multidecadal behavior of the North Atlantic Ocean. Should the current positive AMO (warm North Atlantic) conditions persist into the upcoming decade, we suggest two possible drought scenarios that resemble the continental-scale patterns of the 1930s (positive PDO) and 1950s (negative PDO) drought.
The warm Atlantic cool Pacific pattern causes devastating droughts in the west and the plains with severe consequences on the food supply of the United States. The warm north Atlantic (right 2 figures) is strongly associated with U.S. droughts.
The last time the earth had sustained positive climate forcing like we have now (then from low volcanic activity and positive solar forcing) was the medieval warming period. Research by Prof. Valerie Trouet et al published in Science discovered that the north Atlantic stuck in the warm phase for more than 300 years.
Fig. 1. Proxy-derived long-term NAO reconstruction. (Top) Reconstructed winter precipitation for Scotland and February-to-June Palmer Drought Severity Index (29) for Morocco. Records were normalized over the common period (1049–1995) and smoothed with the use of a 30-year cubic spline. (Bottom) Winter NAO reconstruction NAOms (black curve) is the difference of the Scotland and Morocco records. The gray area is the estimated uncertainty; yellow and red areas are the 10 and 33% highest and lowest values since 1700. The blue line represents the 30-year smoothed Lisbon-Iceland instrumental NAO index series (11).
During the medieval warming period the subtropical highs expanded in the Atlantic and Pacific, the Atlantic warm pool expanded and the storm track moved north on the coast of Europe causing Spain and southern Europe to dry while northern Europe became wetter. Drought persisted across the American southwest. Megadroughts devastated the Anasazi civilization.
The natural climate forcings - a slightly warmer sun and low volcanic activity - that caused the Medieval Warming period are weaker than the anthropogenic forcings that are causing warming now.
The five fold increased in insurance loss rates normalized for inflation are the result of disasters caused by the warm Atlantic phase. Natural oscillations would normally cause the Atlantic to shift between warm and cool phases, but human greenhouse gas emissions are forcing the north Atlantic into a protracted, severe warm phase. This human forced climate change is already producing catastrophic losses for America. Hurricane Sandy is one of many weather disasters tied to the human forced heating of the north Atlantic ocean. Sandy is the 9-11 of 2012.