I was waiting to publish this until the NASA-GISS July global average surface temperature measurement came in and it was 1.18oC above the NASA-GISS benchmark, which works out as 1.436oC above the nineteenth-century benchmark (the one the UN uses), which is itself 1.636oC above 1750 levels (a true measure against pre-industrial times). We are still in the early stages of the El Nino, so a jump well above 1.5oC even against the UN measure should be expected; with a few months possibly close to 2oC. For the first six months of the year we have already reached a global surface temperature which is higher than in 2016, the last El Nino year. The greatest risk is that every time we have an El Nino, as the base temperature gets higher and higher, positive feedback loops will be triggered (e.g. North Pole ice cap, Northern Hemisphere permafrost, peat bogs, Amazon rainforest dieback) which will then take global surface temperatures higher and higher.
Climate Cells
The effect of the warming of the atmosphere varies geographically due to the complexity of the Earth’s climate system. The biggest complexity is the different temperature zones produced by the interaction of the Earth’s shape with the energy from the Sun. At the equator, the Earth’s surface is most directly exposed to the Sun’s energy as it is perpendicular to the Sun and that orientation changes little during the year. As we move more northwards, the Earth’s surface becomes less and less perpendicular to the Sun, so the Sun’s energy has to both travel through more of the atmosphere and hits at a greater and greater angle. This is why the equator is the hottest and the poles are the coldest. Complicating this is the movement back and forth of the Earth’s axis during the year that creates the seasons, as first one hemisphere is exposed more to the Sun and then the other. In June it is the time of the Northern Hemisphere longest day (northern summer solstice), in December the Southern Hemisphere longest day (southern summer solstice) with times in between (March and September equinox) where the Sun is directly above the equator.
With the equator receiving the greatest amount of energy from the Sun, the atmosphere is heated and expands creating an area of lower pressure that sucks up humid air. That air then falls northwards and southwards where the atmosphere expands less (less energy from the Sun due to its greater angle to the Sun), shedding its moisture until it cools and falls to Earth as dry air. The areas where the air sheds its moisture are the tropical wet zones where we find rainforests, as the wet zones have a very consistent climate of high rainfall and high temperatures. This area changes as the Earth moves on its access, creating an adjacent area which has a predictable seasonal wet and a seasonal dry period. Beyond these are the areas which only ever receive the dry air, which is where the Earth’s great deserts exist. At this point the dry air returns to the equator producing a self-feeding circulation, the Hadley Cell.
If the Earth didn’t rotate the Hadley cell would extend all the way to the poles, but because it does the winds produced by the air movement are forced sideways by the friction between the moving Earth’s surface and the body of air; the Coriolis effect. The winds are forced leftwards, creating what we know as the trade winds. The Hadley cell ends around 30o north, and south.
The poles are the places which receive the least Solar energy, and therefore where air cools and falls to Earth creating the lowest atmospheric height. This cold is compounded by the whiteness of the Antarctic ice sheets, and Arctic and Antarctic sea ice, as they reflect much of the Sun’s energy back out to space. The covering of the oceans produces a desert effect, the air is extremely dry. The cool dry then travels southwards, warms, and is some of it is convected upwards at around 60o north and south. The resulting winds are also forced to the left by the Coriolis effect, producing winds from east to west. This circulation is the Polar Cell. At 60o some of the air also continues toward the equator and ends up colliding with the edge of the Hadley Cell at 30o which tends to drag the air down to the Earth’s surface and that air then travels back toward the poles where it collides with the Polar Cell, dragging the air back upwards and completing what is known as the Ferrel (or Mid-Latitude) Cell. In the Ferrel Cell the Coriolis effect pulls the winds to the right, producing the Westerlies (winds travelling from west to east).
As the Earth’s temperature warms, the Hadley Cell will expand more northwards and southwards changing the locations of the wet, wet/dry and dry zones. In Africa some of the Sahel (the dry/wet area) may become much wetter, and some of the dry zone become like the Sahel. These changes will be most beneficial for Sudan, Chad, Niger, Mali, Mauritania. The dry area will expand northwards, across the Mediterranean to Southern Europe – turning highly populated areas of Spain, Southern Portugal, Southern Italy, Greece and Northern Turkey into extremely arid areas. The Southwestern US and the Prairies may also become much more arid, showing the folly of the rapid growth of the past few decades in such cities as Phoenix and Las Vegas. This a projection for 2080-2099 for North American precipitation relative to the present day, with ongoing climate change. With feedbacks, such a future could happen a lot sooner. Central America and the Caribbean may become much more arid. With such reductions in precipitation, and increases inn temperature much of current North American agriculture may become untenable.
Below is a current view of North Africa and Europe. With continuing climate change the light brown desert areas will jump across the Mediterranean and take over Spain, Portugal, Southern Italy, Greece and Turkey.
In the southern hemisphere, northern Namibia and Botswana may benefit but Southwestern South Africa where major population centres exist may get much dryer. The probable impact on biomass in South Africa between 2000 and 2050.
The same will happen to Australia, with the south west of the country seeing rainfall reduced by 40% or more, and even parts of the highly populated south east seeing significant falls in rainfall. The east of each continent tends to benefit from the winds travelling from east to west in this zone, as they bring water from the oceans in the form of storms. In South America, Chile could be especially affected, as well as South West Bolivia and Northern Argentina.
The problem in the wet zones will be the interaction of increased warmth with very high humidity, which may produce “wet bulb” temperatures (the combination of heat and humidity) which are beyond human survivability for any length of time. I experienced this myself while in the southern Costa Rican rainforest where I quickly sweated out my electrolytes and was saved by the carrying of electrolyte tablets. Increased temperature also leads to stronger evaporation and convection, even greater levels of humidity and stronger storms.
Arctic Sea Ice
The greatest risk at the poles in the short term will be reductions in sea ice, as that would expose more and more dark water to the Sun’s energy. The worst case is that the North Pole loses most, if not all of its se ice and turns into a maritime climate. The open water allows for precipitation, which will then fall onto the Greenland ice sheet and the northern permafrost as rain during the summer months, triggering more rapid ice loss and the warming of the permafrost. The latter would expose the plant and animal material within the permafrost to microbial activity that would produce both carbon dioxide (in dry areas) and methane (in wet areas), further increasing the levels of greenhouse gases in the atmosphere. In addition, during winter the maritime environment could produce clouds that block the escape of energy and limit the regrowth of the sea ice. This would then become a self-feeding process leading to less sea ice in the winter and more open water in the summer. The lack of sea ice would also allow for increased waves which could mix the colder less-salty surface waters with the warmer saltier waters below, adding to the inability of sea ice to reform in the winter.
In pre-historic times large forests existed on Greenland, providing proof that such a process could maintain warm Arctic temperatures even in the darkness of the northern winter. The rapid warming of the northern Polar Cell would reduce the temperature gradient between it and the northern Ferrel Cell, threatening to break down the division between the two.
Amazon Rain Forest
The Amazon Rainforest is threatened by the mixture of human destruction, higher temperatures and the possible movement north of the southern edge of the Sahara Desert. The latter provides a flow of nutrients as winds carry nutrient-rich dust from the Sahara to the Amazon. The former reduces the local scale and density of the rainforest, undermining its ability to produce its own weather and to shield the ground from the Sun. Parts of the rainforest have already been turned into grasslands because of this. Measurements made in the past few years already point to the Amazon Rainforest becoming a carbon source rather than a carbon sink. Without the rains produced by the Amazon rainforest many of the areas around it would become much more arid.
Differences Between Northern and Southern Hemispheres
The northern hemisphere will be impacted faster by climate change because there is less ocean to draw in the additional heat into the depths and much more land to be heated up. It is the opposite in the southern hemisphere. In the last “Hothouse Earth” events, (Cretaceous Hot Greenhouse 92 million years ago and the Paleocene-Eocene Thermal Maximum 56 million years ago), the northern hemisphere went Hothouse well before the southern hemisphere. Therefore, probably the eastern side of a southern continents in the temperate zone, and highlands in that zone of the southern hemisphere may be the last places to be heavily affected by climate change; Southern Brazil, Uruguay, North Eastern Argentina, Paraguay, and parts of Bolivia. New Zealand will also be much less affected given the mediating effect of the surrounding ocean waters.
The North Atlantic Cold Blob and Storms of Our Grandchildren
James Hansen has pointed out that the melting of the Greenland Ice Sheet will dump large amounts of fresh water into the North Atlantic. As this water does not contain salt, it will be significantly lighter than the warmer but salty water beneath it and will therefore float on top of the ocean water. This expanding layer of cold light water will create a “cold blob” in the North Atlantic surrounded by warmer waters. The interaction of the cold and warmer waters will create storms, possible very large storms. Hansen hypothesizes that such huge storms were created in the ancient past when the Greenland ice sheet last melted, creating huge waves that could push large boulders high up sea-facing slopes. Such “storms of our grandchildren” (the title of Hansen’s book) could bring brutal weather to the North Atlantic, greatly impeding shipping and battering the coasts around the area. The cold blob would tend to cool the local area, offsetting warming locally until the Greenland ice sheet is fully melted. It could also produce large amounts of snow that will fall upon North Eastern Quebec, Newfoundland, Halifax and the North Eastern US, reflecting back the Sun’s energy. Climate change would bring a local cooling, and massive snow falls, until at least the southern part of the Greenland ice sheet is fully melted. As per below, it is already starting to form.
The Climate and Ice Sheets Can Sprint
The work of paleo-climatologists has shown that the Earth’s climate is capable of jumping from one temperature equilibrium to another over a period of decades, which puts the lie to the notion that the Earth’s climate only changes very slowly. Once tipping points are reached temperatures can change very rapidly. This is the great danger with the ongoing anthropogenic releases of greenhouse gases, we know there are tipping points “out there” but we don’t know how close we are to them. Once tipping points are reached, we may be completely incapable of stopping the climate from moving to a new, hotter, equilibrium within decades. This is the biggest error with the UN climate projections, no account is made for the possibility of such rapid changes. Linear change is assumed rather than periods of linear change interspersed with abrupt jumps.
The same goes for the ice sheets, which are highly complex mechanical structures. When such a structure reaches a critical point a significant part of it may collapse. The ice sheets, especially in the Antarctic are being undermined from beneath by warming waters, becoming cumulatively weaker. A part of the ice sheet may become weak enough to collapse at its front facing the ocean, a collapse which could then release all of the ice in the sheet behind the bolstering front within decades; feet, not inches, worth of sea level rise. Humanity is like someone walking on the edge of a cliff in the middle of fog, not knowing where the edge is. Once over the edge, there is no returning to the cliff.
Marlo Garnsworthy/Geophysical Research Letters
Toasty. Just got to find those sweet spots on Earth where coastal superstorms or inland mega-fires or methane fireballs won't hit and ride it out for a million years. That's a lot of tins of beans and bog roll to stock up on...
This is very good. And very much needed. Philanthropy of the best kind, in that it can be used as a weapon to change. And change is needed to prevent the catastrophe inherent in the runaway train of the capitalist economy from occurring.