An international team of researchers from United Kingdom, Denmark, and Germany have revealed, that during periods of increased solar irradiance, the trade winds weaken and the Walker circulation in the tropical Pacific shifts eastwards.

An international team of researchers from United Kingdom, Denmark, and Germany has found robust evidence for signatures of the 11-year sunspot cycle in the tropical Pacific. They analyzed historical time series of pressure, surface winds, and precipitation with specific focus on the Walker Circulation – a vast system of atmospheric flow in the tropical Pacific region that affects patterns of tropical rainfall. They have revealed that during periods of increased solar irradiance, the trade winds weaken and the Walker circulation shifts eastwards.

Stergios Misios, a postdoctoral researcher at the University of Oxford, said “We deal with a very short record of observations in the tropical Pacific and we must be very careful with how we filter out other interannual fluctuations. After a careful treatment of the data covering the last 60 years, we detected a robust slowdown of the Walker cell during years associated with solar-cycle maxima”. The analysis shows that, in tandem with changes in the wind anomalies, the dominant patterns of tropical precipitation shift to the central Pacific during solar-cycle maxima. As a result, rainfall decreases over Indonesia and in the western Pacific, and increases over the central Pacific Ocean.

Simple mechanisms amplify the solar signal

The issue of solar influences on climate is long and controversial as there have been numerous claims which in most of the cases did not survive proper statistical scrutiny. But besides statistical verification lies an even more challenging problem: how miniscule changes in incoming solar radiation could produce significant climate signatures?

“Soon enough, we realized that the magnitude of the wind anomalies that we detected in observations simply could not be explained by radiative considerations alone. We thought that if it comes from the Sun, there must be another mechanism that amplifies the weakening of the Walker circulation.” said Prof. Lesley Gray of University of Oxford. With the aid of a global climate model, this mechanism was found in the dynamical coupling between the atmosphere and ocean circulation in the tropical Pacific.

Averaged over the globe the surface temperature imprint of solar cycle barely reaches 0.1 K in a solar maximum – almost 8 times weaker than the global warming trends observed in the 20th century. Yet, even such a weak surface warming influences the Walker circulation through changes in global hydrology. As the surface warms, water vapor in the atmosphere increases at a higher rate than is lost by precipitation, necessitating a weakening of the Walker cell. This is a well-tested mechanism in model simulations of increased CO2 concentrations but it turns out that is operating under the 11-year solar cycle, too.

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The post New Paper: Solar Variability Weakens Trade Winds appeared first on The Global Warming Policy Forum (GWPF).

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March 29, 2019 at 06:23AM

It’s a good thing they’re not trying to control lives or central planning or some such~ctm Chalmers University of Technology A sixth of all emissions resulting from the typical diet of an EU citizen can be directly linked to deforestation of tropical forests. Two new studies, from Chalmers University of Technology, Sweden, shed new light…

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March 29, 2019 at 06:09AM

Credit: NASA – GISS

Showing once again that significant warming and cooling are normal features of the global climate over thousands of years and longer. We could speculate whether this particular research might be linked to the de Vries cycle.

The warm waters of the Gulf Stream flow up along the east coast of North America, moderating the climate of vast areas of northern and western Europe, says Phys.org.

Once the Gulf Stream gets far enough north, the warm waters cool.

As they cool, they sink and start flowing south, forming what scientists call the North Atlantic Deep Water.

Nick Balascio explained that the Gulf Stream/Deep Water system is known as the AMOC, or Atlantic Meridional Overturning Circulation.

Balascio, an assistant professor in William & Mary’s Department of Geology, is a member of a group of scientists that found evidence that changes in the strength of AMOC can serve as an precursor to massive future climate changes.

Their findings were published in the journal Nature Communications in a paper “Deep-water circulation changes lead North Atlantic climate during deglaciation.” Deglaciation, or the widespread melting of glaciers, have triggered massive shifts in climate.

Balascio explains that the team’s evidence shows that a strengthening in the AMOC flow was a precursor to a sudden warming trend about 11,000 years ago.

Conversely, a weakening AMOC was followed by what is known as the Younger Dryas stadial, a major cooling period about 13,000 years ago. Balascio pointed out that each shift in AMOC strength preceded the climactic shift by the same amount of time—around 400 years.

He also noted that the AMOC has been weakening once again for the past century or so. The paper indicates that once the Younger Dryas settled in, air temperatures in Greenland dropped by about six degrees.

“These results suggest that changes in ocean circulation precede major global climate events,” he said. “So we should therefore take seriously the evidence that suggests the AMOC has been slowing down over the past century or more.”

The team recorded the relative strength of the AMOC and the development of the Deep Water Formation through comparison of various coring samples of ice and sediment from various points across the North Atlantic, including sites from the land, ocean and lakes.

“Each record provides one piece of the puzzle,” Balascio said. “So each record provides information on a different aspect of the climate system such as past atmospheric temperatures and surface ocean conditions.”

Full report here.

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March 29, 2019 at 05:21AM

By Paul Homewood

Another thorough assessment of wildfire trends wrecks alarmist claims:

ABSTRACT

Wildfire has been an important process affecting the Earth’s surface and atmosphere for over 350 million years and human societies have coexisted with fire since their emergence. Yet many consider wildfire as an accelerating problem, with widely held perceptions both in the media and scientific papers of increasing fire occurrence, severity and resulting losses. However, important exceptions aside, the quantitative evidence available does not support these perceived overall trends. Instead, global area burned appears to have overall declined over past decades, and there is increasing evidence that there is less fire in the global landscape today than centuries ago. Regarding fire severity, limited data are available. For the western USA, they indicate little change overall, and also that area burned at high severity has overall declined compared to pre-European settlement. Direct fatalities from fire and economic losses also show no clear trends over the past three decades. Trends in indirect impacts, such as health problems from smoke or disruption to social functioning, remain insufficiently quantified to be examined. Global predictions for increased fire under a warming climate highlight the already urgent need for a more sustainable coexistence with fire. The data evaluation presented here aims to contribute to this by reducing misconceptions and facilitating a more informed understanding of the realities of global fire.

https://royalsocietypublishing.org/doi/full/10.1098/rstb.2015.0345

This section is particularly relevant:

3. Have fire impacts increased in many regions around the globe?

(a) Fire intensity and severity

While the trends in area burned explored above have implications for the effects of fire on global carbon emissions, ecosystems and society, the spatial extent of burning is not always closely linked to the impacts of a fire. From a perspective of fire ecology or risk to infrastructures, the intensity of a fire (i.e. its rate of energy output), its severity (its ecosystem impacts) and its spatial patterns (degree of patchiness) may be more important than the total area burned. For example, the degree of vegetation consumption, the depth of burning into the organic and mineral soil, and the proximity of areas less affected or not by fire are key in determining the length of time for a burned area to ‘recover’¹ [3,61–63]. The notion that fire intensity and severity have increased in recent years pervades media reports and some of the literature [11,64–66]. Whether or not this is the case is not easy to ascertain given that these parameters and associated trends are much more difficult to determine compared with area burned. All else being equal, fire intensity can indeed be expected to increase with air temperature [67], and it can be deduced that areas that are experiencing higher atmospheric temperatures in the fire season associated with global warming would experience more intense fires. For example, the catastrophic 2009 Black Saturday fires of Victoria (Australia) were reportedly associated, among other factors, with unprecedented high atmospheric temperatures (since measurements began) and fire intensity [68]. Whether or not this extreme event signifies a trend or may simply be the result of longer-term natural variability in fire behaviour remains an open question. Indeed, it has subsequently been suggested that the fire weather potential witnessed during Black Saturday and the associated level of fire intensity was not unprecedented in southeastern Australia [69].

Few studies exist that have explicitly examined trends in fire severity. These have mainly focused on the western USA, an area where there are particular concerns about increased fire activity [42,70]. Examining trends from 1984 to 2006 for large ecoregions in the north- and southwest USA, Dillon et al. [71] found no significant increase in the proportion of annual area burned at high severity for five of the six regions considered, with the southern Rockies being the exception. For the Sierra Nevada region (California), which was not covered in the previous study [71], Hanson & Odion [72,73] found no general increase in fire severity within the period 1984–2010. Considering ten national forests in California for the same period, Miller & Safford [74] found a significant increase in burn severity for yellow pine–mixed conifer forests. They attribute this largely to decades of fire suppression and other management practices rather than climate, which have led to major changes in forest composition and structure, increases in density and fuel-loading, and hence fire behaviour. Covering the much larger area of the dry forest landscapes of the western USA, including large parts of those examined in the aforementioned studies, Baker [75] found that the rate of high-severity fire in the period 1984–2012 was within or below that of historical century- to millennial-scale estimates.

Thus, while there is evidence of a recent increase in proportional fire severity for a specific forest type in California, these independent studies do not support the notion of an overall increase in fire severity over the past few decades in the fire-adapted forested landscapes in the western USA. Indeed, a longer term perspective focused on the Californian Sierra Nevada and Cascades by Mallek et al. [49] suggests that the annual area burned at high severity between 1984 and 2009 was only half that prior to European settlement (approx. 1500–1850), associated with an overall smaller area burned compared to pre-European times. Whether or not the overall lack of change in burn severity applies also to other regions where perceptions of increases in fire severity exist too has to remain unanswered until robust data emerge to test this notion.

 Time after time, forestry experts  tell us that wildfires are not getting worse because of climate change, that from a historical perspective current wildfire activity is not unusual, and that we are now seeing the results of decades of fire suppression and poor forest management.

I predict that David Attenborough’s upcoming programme on climate change will highlight forest fires in California and maybe Greece. He will wheel on Michael Mann to “explain the science”. Mann, who of course knows nothing at all about forestry or most of the other things he opines about, will waffle on about droughts, heatwaves and beetles, and then blame them all on global warming.

At no stage though will Attenborough consult the experts who actually know about forests and wildfires.

I wonder why?

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March 29, 2019 at 04:21AM