Posts Tagged ‘AMO’

Little Ice Age was due to low solar irradiance

March 10, 2014

The Sun is the only real source of energy available at the surface of the earth (and any heat from nuclear reactions at the earth’s core is extremely small if not completely negligible). That the oceans have a much higher heat capacity than the atmosphere at the surface of the earth is obvious. It seems also fairly clear to me that it is the dynamics of ocean – atmosphere interactions which control climate and weather. And it is the oceans and long time scales which dominate climate while it is the atmospheric variations and short time scales which determine weather.

But the driver is always the Sun.

A new paper in Nature GeoScience “used seafloor sediments taken from south of Iceland to study changes in the warm surface ocean current. This was done by analysing the chemical composition of fossilised microorganisms that had once lived in the surface of the ocean. These measurements were then used to reconstruct the seawater temperature and the salinity of this key ocean current over the past 1000 years.”

The researchers found that ” low solar irradiance promotes the development of frequent and persistent atmospheric blocking events, in which a quasi-stationary high-pressure system in the eastern North Atlantic modifies the flow of the westerly winds. We conclude that this process could have contributed to the consecutive cold winters documented in Europe during the Little Ice Age.”

Paola Moffa-Sánchez, Andreas Born, Ian R. Hall, David J. R. Thornalley, Stephen Barker. Solar forcing of North Atlantic surface temperature and salinity over the past millenniumNature Geoscience, 2014; DOI: 10.1038/ngeo2094

AbstractThere were several centennial-scale fluctuations in the climate and oceanography of the North Atlantic region over the past 1,000 years, including a period of relative cooling from about AD 1450 to 1850 known as the Little Ice Age. These variations may be linked to changes in solar irradiance, amplified through feedbacks including the Atlantic meridional overturning circulation. Changes in the return limb of the Atlantic meridional overturning circulation are reflected in water properties at the base of the mixed layer south of Iceland. Here we reconstruct thermocline temperature and salinity in this region from AD 818 to 1780 using paired δ18O and Mg/Ca ratio measurements of foraminifer shells from a subdecadally resolved marine sediment core. The reconstructed centennial-scale variations in hydrography correlate with variability in total solar irradiance. We find a similar correlation in a simulation of climate over the past 1,000 years. We infer that the hydrographic changes probably reflect variability in the strength of the subpolar gyre associated with changes in atmospheric circulation. Specifically, in the simulation, low solar irradiance promotes the development of frequent and persistent atmospheric blocking events, in which a quasi-stationary high-pressure system in the eastern North Atlantic modifies the flow of the westerly winds. We conclude that this process could have contributed to the consecutive cold winters documented in Europe during the Little Ice Age.

Cardiff University Press Release:

Changes in the sun’s energy output may have led to marked natural climate change in Europe over the last 1000 years, according to researchers at Cardiff University. The study found that changes in the Sun’s activity can have a considerable impact on the ocean-atmospheric dynamics in the North Atlantic, with potential effects on regional climate.

Scientists studied seafloor sediments to determine how the temperature of the North Atlantic and its localised atmospheric circulation had altered. Warm surface waters flowing across the North Atlantic, an extension of the Gulf Stream, and warm westerly winds are responsible for the relatively mild climate of Europe, especially in winter. Slight changes in the transport of heat associated with these systems can lead to regional climate variability, and the study findings matched historic accounts of climate change, including the notoriously severe winters of the 16th and 18th centuries which pre-date global industrialisation.

The study found that changes in the Sun’s activity can have a considerable impact on the ocean-atmospheric dynamics in the North Atlantic, with potential effects on regional climate.

Predictions suggest a prolonged period of low sun activity over the next few decades ……..

Though their study has nothing whatever to do with global warming and any man-made effects they still feel it necessary to add this caveat (presumably because the reviewers, and the Journal, or both, insisted).

Predictions suggest a prolonged period of low sun activity over the next few decades, but any associated natural temperature changes will be much smaller than those created by human carbon dioxide emissions, say researchers.

Global cooling indicators are increasing

January 23, 2011

The conditions in the relatively thin, chaotic surface layer of atmosphere surrounding the earth within the earth-sun system are what we call climate in the long term over large geographic regions and what we call weather in the short term over small geographic regions. I am convinced that these conditions are dominated by the sun and that the primary vehicles for transporting energy around the earth’s surface (and which is decisive for the chaotic boundary layer) are the oceans. The energy carrying capacity of the atmosphere is small compared to that of the oceans.

The major ocean cycles which seem to be most relevant are the Atlantic Multidecadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO). The El Niño-Southern Oscillation (ENSO) seems to be superimposed on the major cycles which which may even derive from ENSO and the deep ocean circulation patterns. The major cycles also contain sub-cycles such as the Nothern Atlantic Oscillation (NAO) or the Southern Oscillation Index (SOI). There are other minor cycles such as the Arctic Oscillation Index (AO) and the Antarctic Oscillation (AAO).

The indicators that we are in a period of 20 – 30 years of global cooling are increasing:

1. The quiet sun is perhaps the most important indicator we have that we are entering (or have entered) a global cooling period. The period 2000 – 2030 could well be similar to that during the Dalton Minimum between 1790 – 1820.

Image Attachment

graphics credit: sc25.com

2. There have been regular periods of warming and cooling in the past.

Alternating periods of warm and cooler weather have been with us as far back as our climate records go. Some of the past cooler periods have been more severe than others, like the Sporer, Maunder and Dalton Minimums. Professor Don Easterbrook has documented some 20 such cool periods over the last 500 years

Figure 1

graphic: Don Easterbrook

3. Taking just the main ocean cycles, the AMO is a 66 year cycle.

AMO peaks occurred on May 1878 and November 1944. The next peak is forecasted to occur in April 2011. The last trough occurred in January 1978, and the next trough is expected to occur in June 2044. As we see here, the length of a complete cycle is about 66.5 years.

The AMO went positive in 1994 and actually peaked in July 2010 and is now on its way down. It should go negative sometime in 2015 and remain negative till about 2048.

4. The Pacific Decadal Oscillation (PDO) has a shorter cycle of about 60 years.

graphic: digitaldiatribes.files.wordpress.com

The PDO cycle is not quite as long as AMO. Because the periods differ, their peaks and troughs will vary relative to each other. This has an interesting long-term result in terms of warming and cooling. The PDO had a peak in the function in October 1929 (about 15 years prior to AMO). The next peak occurred May 1990 (about 21 years prior to the anticipated AMO peak). The period here is about 60.5 years.

PDO has gone negative since September 2007  and will remain in negative territory probably for the next 30 years. For about 2 decades the PDO and the AMO will both be negative (but as can be seen above the amplitude of the short term variations are so large that short periods in the positive region are perfectly possible and inevitable, even while the long term average is negative or vice versa.)

5. ENSO and the efects of La Niñas and El Niños.

Returning to Matti Vooro’s article:

During negative or cool phases of PDO and AMO, there are more La Niñas than during the positive phases. This contributes to more cold winters and colder years during negative PDO. During positive or warm phases of PDO and AMO, there are significantly more El Niños. This is why there is more warming when the PDO is positive. The current negative or cool PDO and the La Niña are why we have had all the recent cold weather. The La Niña’s may have directly contributed to the Red River Flooding of 2009 and the recent flooding in Australia and Brazil.

…. The AMO is affected by ENSO cycles, especially El Ninos, so we saw a brief warming of AMO during 2010. Climate history shows that global cooling was strongest when both the PDO andAMO were both simultaneously in the negative or cool mode – like in 1964-1976 and again 1916 to 1923. The AMO cycles have been quite variable. During its last cycle it was in the negative or cool mode for 30 years (1964-1994] and its cycle seems to be related to the Meridional Overturning Circulation [MOC] and the changes in the Atlantic Thermohaline Circulation [THC]. There are a number of estimates when it will again go negative. My best estimate is about 2015 based on the most frequent past intervals of around 20 years and the cooler waters that feed the MOC from the Southern Oceans. Once it does go negative, the global temperature anomalies may drop further until about 2030, the Arctic temperature may cool further and the Arctic ice extent should increase again.

Professor Easterbrook has made a global forecast for temperature:

The IPCC projections are no longer credible but it must be borne in mind that these projections had little to do with actually bringing science to make the best forecast possible but instead were focused on poltical objectives; it seems mainly to redistribute wealth and to demonise CO2 so as to drive the carbon trading market.

That global cooling is upon us seems more and more likely and I apprehend that Easterbrooks’s lowest curve will materialise and show that the current Landscheidt minimum will be comparable to the Dalton minimum.



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