This is an enhanced version of an essay that became the source for a talk that I gave to the Atheist Society in Melbourne on 10 September 2013.
If it is true that we are all causing global warming and consequent significant changes to global climates, then the issue is vitally important for everybody. But many people don’t accept that global warming is occurring, and some who see it occurring don’t accept that it is caused by human action. They sometimes say that anyone who wants action to reduce global warming is an extremist in the religion of unreliable science, “which is only a theory”.
One specific claim is that the explanation of how the current warming is caused is false and that scientists are just promoting it to keep themselves in jobs, and/or that there are other explanations that do not include human action. This includes a few scientists who have not studied the relevant phenomena, and think they don’t need to. Another slant to this claim is that our fate is in God’s hands, not in ours. If humanity is to suffer a great calamity it will be a punishment for our wrongdoing.
People who have an open mind on the matter often find it hard to accept that human action is rapidly changing the global climate. There are three reasons for this. The first is that there were continual climate changes and extreme weather conditions long before human beings had any significant impact on the environment, so there would seem to be no need to blame humanity. This makes it easy to pick a range of events and make a plausible case that any present warming is caused by something other than human action. To get a clearer picture of the relevance of these earlier events it is necessary to put them into context and to examine the details. This will show that the current situation is quite different.
The second reason for rejecting the occurrence of global warming is that that global warming happens to cause unusually cold weather in some parts of the world, which might suggest that, overall, warming is not occurring.
And the third reason is that climate science is very complex and some relevant things are unknown. The unknown things range from the future actions people may take in addressing or ignoring the matter, to details about the conditions of the land and sea, including future earthquakes and volcanoes. This makes predicting all the effects of warming very difficult. So the pronouncements of climate scientists often seem contradictory and hard to understand or believe. It also means that there are enough unexpected kinds of climatic affects for a list of carefully selected examples to be presented as a plausible scientific case that global temperatures are not increasing.
However, the natural processes that lie behind the continual changes to climate and weather have been well established by repeated rigorous scientific investigation. Also, the large-scale predictions have been remarkably accurate. But there will always be critics who will quickly point to and exaggerate the significance of any minor or apparent errors.
What is usually referred to in public discussion as “Climate Change” really involves three distinguishable concepts: global heating; global warming; and climate change. Global heating is the most basic process. After some delay, global heating results in perceptible warming around the globe. Global warming affects the climate around the globe. All these processes are complex and their outcomes are often unexpected.
There are many physical systems that affect the earth’s climate but only the more significant ones are covered in this discussion.
In this context, heating means the addition of heat. Heat is a form of energy. Energy is continually being converted from one form to another. So when I use the word heat, sometimes I will be referring to some other form of energy that will be converted to or from heat.
The various forms of energy are:
- electromagnetic radiation, such as sunlight and radio waves;
- chemical energy, where substances react to make things hotter or to produce electricity;
- electrical energy;
- the energy inside atoms;
- gravitational energy;
- the inherent energy of matter, in accordance with Einstein’s well-known equation, e = mC2;
- and the energy of moving objects.
The heat energy of an object or a liquid or a gas is the energy of the motion of the atoms and molecules it contains. Heat is in everything that is warmer than a temperature called absolute zero. Anything that was at absolute zero, -273 degrees Celsius (or 0oK), would contain no heat whatever. So ice, and liquid nitrogen (-196oC), etc., contain heat.
Global heating (or more strictly, nett global heating) means that more heat is getting into the earth’s surface than is getting out. Nett global heat reduction means that less heat is getting in than getting out. What is meant here by the earth’s surface is the land, the seas, the atmosphere, and everything in them.
Heat comes into the earth’s surface mainly as radiation from space. A minor source, less than one percent, is from the interior of the earth, some of which is steady conduction from the earth’s mantle through the crust and some is through breaches in the crust in the form of volcanos, hot springs and vents in the sea floor.
Heat goes out from the earth’s surface as radiation into space.
Almost all the radiant energy that reaches the earth from space comes from the sun. The radiation from stars, planets, the moon, etc., is insignificantly small.
The radiation from the sun is emitted in all directions, with only a very small proportion directed towards the Earth. The amount emitted is not constant. Its variations are mostly comparatively small but still large enough to have short-term and cumulative effects on the earth. The variations include sunspots, solar flares and ejections of hot matter, each having specific types of effect on the earth in addition to heating.
Sunspots are readily observed from Earth. Their number and duration increase and decrease cyclically, with the lengths of individual cycles ranging from about nine to thirteen years. The total amount of energy emitted by the sun increases and decreases during each cycle, closely in step with the number of sunspots.
In addition to these cycles, there are also periods, called Grand Minimums, when the emission of radiation from the sun is abnormally low. One such period known as the Maunder Minimum coincided with the Little Ice Age that affected Europe from about 1645 to 1715. There was another minimum from the late 1800s to the early 1900s, which was followed by a maximum at about 1950. Since then emissions have been decreasing (which is why people were expecting global cooling a few decades ago). The decrease has been sharper this century. Some solar astronomers think the decrease will continue towards another grand minimum, but as yet there is no basis for predicting the sun’s output of radiation.
The earth’s path around the sun is an ellipse not a circle. So the earth moves further from the sun and then closer twice during each year, i.e., during each revolution around the sun. The proportion of solar radiation that reaches the earth decreases as the earth moves further from the sun. Also, the elliptical orbit slowly gets longer and thinner, and then shorter and fatter, in a 100 000 year cycle. The longer the ellipse, the less total annual radiation reaches the earth. So the proportion of the sun’s heat that falls on the earth varies in a complex cyclic pattern.
Some of the sun’s energy that reaches the earth at ground level is absorbed, causing an increase of heat. Some is reflected from the land and sea. Some does not reach ground level but is reflected back into space by clouds high in the atmosphere, or is absorbed by clouds, which it heats.
Also, particulates – tiny solid particles suspended in the air – reflect incoming radiation away from Earth, and some absorb the radiation and are heated. Overall, this reduces global heating. Until recently almost all of the particulates were from natural causes, such as dust carried by the wind, smoke from fires lit by lightening, ash from volcanic eruptions, and dust from impacts by objects from outer space. In 1991, the particulates from the eruption of Mt Pinatubo in the Philippines blocked enough solar radiation to cause a nett heat loss, and to cause the global temperature to be lower than the previous year, in contrast to the general continual increase that occurred earlier and later. There have been occasions when the dust from volcanos or from impacts from space stopped most of the sunlight from reaching ground level for long enough to severely affect the climate and to cause widespread devastation. Such an event in the 13th century caused a short “mini ice age” that lasted for some decades.
Exhaust from internal combustion engines, smoke from the generation of electricity using fossil fuels, and dust from agricultural and industrial activities add to the amount of particulate material in the atmosphere. Over recent decades there has been a dramatic increase in the amount of particulates in the air. The increasing cooling effect of this is now noticeably slowing global warming.
The amount of solar radiation that is reflected by the earth depends on the kind of surfaces that the radiation strikes. Shiny surfaces such as ice and dry sand and some clouds reflect a lot of the radiation they receive. Dark surfaces like the sea and vegetation absorb a lot of the radiant energy, that is, a lot of heat.
Radiation is more likely to be reflected when it hits a surface at a glancing angle, and most likely to be absorbed when it hits at a right angle. So reflection is greater in areas near the poles than in areas near the equator. Also, areas where there is a slanting incidence get less incoming radiation per area of surface than places that get more direct radiation. And since the axis of rotation of the earth is not at right angles to the plane of revolution around the sun, the north and south hemispheres receive alternately more and less radiation during each year, which causes the seasons, and also gives the polar regions winters with no daylight. This allows extensive areas of ice to form at the polar regions in winter. This then causes greater reflection of solar radiation during other seasons, which reduces the melting of polar ice in summer.
The size of the area that has sunless periods during winter depends on the angle of tilt in the earth’s axis of rotation. This angle ranges from between 22.1 degrees and 24.5 degrees on a cycle of about 41,000-years. So this influences the polar regions to grow and shrink, causing greater or less reflection of solar radiation during this cycle. The present angle is 23.44 degrees and it is getting smaller. But even this tilt of the axis has further complications, the most significant being that the earth’s axis of rotation continually changes the direction in which it leans. From a position of leaning forward, it slowly turns towards the sun then towards the back then outward continuing on with a cycle of about 26 000 years. This slightly modifies the cooling affect of the tilt.
From time to time all or most of these effects coincide in increasing or decreasing the amount of heat from the sun that reaches the surface of the earth, but this is not sufficient in itself to cause long-term heating or heat loss.
While only the half of the earth’s surface that is facing the sun receives solar radiation at any one time, the earth itself is radiating energy 24 hours per day from all surfaces. Most of the radiant energy from the sun is in the visible and ultra-violet wavelengths, but the radiation from the earth is in the much less energetic infrared. (Everything that contains heat, i.e., at a temperature above -273 degrees Celsius, radiates heat, so polar ice is always radiating heat.)
The amount of heat radiated from a surface depends on the surface temperature, and increases as temperature increases (proportional to fourth power of its absolute temperature, i.e., its temperature relative to absolute zero). The amount of heat radiated also depends on the type of surface that is radiating. In general, a surface’s efficiency of radiating energy matches its efficiency of absorbing energy. A wide range of frequencies is radiated at any temperature, but the lower the temperature the lower (and less energetic) are the frequencies.
Not all the heat radiated from the earth gets through into outer space. The transmission of radiation through clouds, and the reflection, and the absorption as heat, depend on the type of cloud and on the wavelength of the radiation. Some clouds and atmospheric gases that let the sun’s radiation through to reach ground level will reflect some of the upward radiation back down again.
Clouds are formed when water vapour in the atmosphere condenses onto solid particles, microorganisms and certain types of molecules in the upper atmosphere. Measurements show that when temperatures increase, more water vapour goes into the atmosphere, allowing more clouds to form. This is reinforced by the fact that warmer air can carry extra water , but slightly offset by the fact that warmer air neds to hold more water vapour before becoming saturated and able to condense.
So, overall, clouds block some radiation from the sun, but also have a greenhouse effect. At present the overall global effect of clouds is thought to be moderate cooling. But there are many kinds of clouds, and some have an overall warming effect. Global warming will cause more clouds, and some scientists think that the overall effect of clouds will become heating rather than cooling.
There is some evidence that the formation of clouds can be enhanced by cosmic rays from outer space, and measurements show that the incidence of cosmic rays has increased over recent decades. But this effect occurs at high altitudes where the air is very “thin” and unable to hold enough cloud to influence global heat increase or loss.
The most important heating effect is caused by molecules of certain gases in the atmosphere, known as greenhouse gases. These absorb and re-radiate the energy radiated by the earth. The effect is dependent on the type of gas, each gas being affected by a different frequency of radiation. This re-radiated energy from the gases is transmitted uniformly in all directions, so about half of it is directed back towards the earth. More greenhouse gas in the air results in more of the radiation being sent back to earth.
The main greenhouse gases are carbon dioxide (CO2), methane, water vapour, and nitric oxide. CO2 is produced by the burning or chemical breakdown of materials containing carbon, i.e., of carbon itself and most organic substances. These processes include the digestive systems of living organisms. The burning of materials containing carbon provides almost all of the energy used by human beings.
CO2 is also produced by the decomposition of carbonates such as limestone. It is also a component of volcanic eruptions.
Much of the CO2 emitted into the air becomes dissolved in the waters around the earth and a lot is taken up by photosynthesising organisms on land and in the sea. The remainder, less than a third, stays in the atmosphere for an average of nearly 100 years.
Over very long periods of time, the actions of marine organisms and natural processes have used up CO2, manly by converting it to calcium carbonate, which becomes limestone rock and other minerals. This allowed the surface of the earth to cool. Over time, tectonic action (i.e., “continental drift) exposed the rocks to organisms whose actions released the CO2 back into the atmosphere, causing the greenhouse effect to heat the surface of the earth. Also, plants and other organisms that absorb CO2 convert it into cellulose and other materials that can “lock it up” while they are alive, and also after they die if their bodies do not decompose or get burnt. This is the source of the fossil fuels that we are now burning in great quantities and so releasing CO2.
There have been claims that greenhouse gases are not the principal cause or global heating. There are also claims that if CO2 is in fact a major cause of heating it has now reached a level of concentration beyond which its effect will no longer increase global heating. Neither of these claims is true. The greenhouse effect has been demonstrated by experiment. It has also been demonstrated that the effect of CO2 does indeed continue to increase global heating at concentrations vastly higher than present levels.
A striking example of this is the planet Venus, whose average temperature, about 460o Celsius, is appreciably higher than the maximum temperature of the planet Mercury. Mercury is the closest planet to the sun, and would be expected to be hotter than Venus. Venus has an atmosphere composed almost completely of carbon dioxide, with traces of nitrogen. Mercury has no atmosphere. Mercury has a hot side that always faces the sun and its maximum temperature is about 430o Celsius. And Mercury has a cold side that is in shade and whose temperatures go down to about minus 170o Celsius. Celsius. So higher concentrations of carbon dioxide are indeed more powerfully effective causes of global warming than are lower concentrations.
But even if this claim of a peak effect were true, since CO2 remains in the earth’s atmosphere for about a hundred years, the more we put in now the longer we will have to wait for its concentration to start going down to a level where the earth’s output of heat is no longer below the input.
Methane is produced mainly as a product of decaying vegetable matter, including digestion by organisms. A molecule of methane has about 25 times the greenhouse effect of CO2, but there is much less methane and it stays in the air for an average time of about 12 years.
Water vapour, which is a major greenhouse gas, is produced in copious amounts by evaporation from the surface of seas, lakes and rivers. Some of the vapour becomes cloud and subsequently rain. The rest remains as greenhouse gas. The amount of water vapour in the air increases when the surface temperature of the water increases and also when the temperature of the air close to the surface increases.
Nitric oxide, which is a less significant greenhouse gas, is produced in high-temperature combustion of carbon-rich compounds in air, as, for example, in internal combustio engines.
The Global Balance
All the processes that produce heat gain and heat loss to the earth’s surface are continually varying. But there is evidence that for at least a billion years the gain and loss of heat in the surface of the earth have been fairly even balanced: the average global temperature has fluctuated less than 10 degrees Celsius above or below present temperatures. This has been enough for the surface to be sometimes largely covered with ice and sometimes to have hardly any ice. Such changes in nett global heating are caused by changes in the amount of greenhouse gases in the atmosphere. Short term minor variations occur when the effects of the other influences coincide one way or the other. At the moment, these are not coinciding sufficiently to be an alternative cause of global heating.
Global Warming – and Cooling
Warming and cooling mean increase and decrease of temperature. Temperature could be thought of as the “pressure” of heat. The bottom of a tall thin vessel of liquid would be at a higher pressure than the bottom of a larger shallow vessel with the same amount of liquid. In the same way small piece of iron that was hot (“higher pressure”) could contain the same amount of heat as a larger cooler piece. So warming is not the same (in this context) as heating, just as water pressure is not the same as the quantity of water. But for any particular vessel, if more water is put in and the water level rises the pressure at the bottom of the vessel will increase.
On Earth, the temperatures of the land, atmosphere and sea are very different at different places around the globe, and at different elevations and depths, and at different times of the year, and at different at times of the day. Global temperature is a notional average of air temperatures around the world at ground level. So quoted global temperatures are tricky compromises. Think of stock exchange indexes and the CPI. (But stock exchange indexes refer to particular points of time not daily averages. And global temperature calculations relate to temperatures of the air at ground level, so do not take into account the temperature of the oceans at various depths or of polar and glacial ice.)
Just as a rise or a fall of the stock exchange does not produce rises or falls in all stocks, rises and falls in heat gain or loss do not produce uniform warming or cooling around the globe. Global heating produces temperatures that show progressive warming in some places, cooling in some places and little change in others. This leads some people to conclude that there is no global warming. But the actual temperatures that are measured around the globe throughout the year show that the weighted average global temperature is increasing.
The local temperature changes that result from global warming and cooling are not necessarily in the same places as the gains and losses of heat. Heat is continually being transported around the globe by winds and ocean currents. Winds are typically seasonal: they are influenced by the changing local and regional temperatures of the land and sea. In many places they are continually changing in strength and direction throughout the day.
Ocean currents are more consistent throughout the year and from year to year.
So local temperatures depend on both the direct nett heat input or loss, and the heat transported to and from other regions. Warming in some regions may cause cooling in others as a result of changes to winds and currents. In particular, this has caused colder weather in areas adjacent to polar regions of the Northern Hemisphere where polar warming has changed the winds and ocean currents.
Processes that Delay Global Warming and Cooling
Various types of “buffers” cause a delay between global heating and its resultant warming of the atmosphere.
The oceans cover about 71 percent of the earth’s surface. But because they are more absorbent of the incoming heat than the land surfaces, the oceans take about 90 percent of the absorbed heat. Water has a high specific heat, for example, it takes nearly ten times the amount of heat to increase the temperature of water by one degree than is needed to heat the same mass of iron by one degree. The average depth of the oceans is about 4000 metres, and since there is some mixing between the different depths of the ocean the absorbed heat does not all stay in the surface layer. So for these two reasons, the increase in the temperature of the oceans has been significantly less than the increase of temperature on the land, even though the oceans absorb most of the radiant heat that reaches the earth’s surface. So the oceans have an enormous buffering effect against both global warming and global cooling.
The warmer surface layers that absorb the sun’s heat then warm the air above them and this causes winds that blow over both land and sea. Sometimes the warmer surface layers are quickly swept down by turbulence in parts of the ocean, and cooler water is pushed up to the surface. This cooler water then cools the air in that particular area.
Global warming and cooling are delayed also by less erratic processes in which heat is stored or released depending on environmental conditions. These buffers are not uniformly spread around the earth, which adds to the complexity of the distribution of warming and cooling.
Some incoming heat is absorbed by ice. This warms the ice and converts some of it into water. Some incoming heat that is absorbed by water converts some of the water into water vapour. Warmer air and oceans also promote the melting of ice. These processes use up heat energy and reduce the amount of warming caused by the heat input. In the reverse process, heat loss will cause some water vapour to be converted to liquid water, and liquid water to be converted to ice.
As much heat is needed to convert ice at 0o C to water at 0o C as is needed to increase the temperature of water by 80o C. This stored heat is known as latent heat. The latent heat absorbed in the conversion of water to vapour is almost seven times the latent heat of melting. These two types of latent heat affect the weather and the climate.
(Latent heat is used domestically in iceboxes, where melting ice absorbs heat and keeps drinks cool. In evaporative air conditioners warm air is cooled by being blown over water, some of which evaporates.)
When polar ice absorbs heat and melts, the melt water is colder than the surrounding seawater, thus delaying the warming of the sea. When rain or water vapour comes in contact with ice, as in polar regions and mountaintops, it is frozen, and the latent heat of freezing increases the temperature of the ice.
So global heating can melt large amounts of ice without any significant increase in global temperature. In the Antarctic, ice is continually forming, but much more continental ice in Antarctica is warming and melting. The cold melt water (which stays on the surface because it is not as dense as the warmer salty water below it) and the cold winds from Antarctica then slow the melting of the sea ice. So the sea ice in the Southern Ocean has generally been increasing. But in some years the amount of sea ice may unaccountably decrease.
Chemical buffering by plants and microorganisms
When sunlight is absorbed by plants and some microorganisms, some of it is used to provide energy for chemical reactions. Processes driven by photosynthesis convert CO2 and water, along with nitrogen and minerals, into the organic chemicals that are used in the body structures of these organisms. These materials become stores of energy. The bodies of these organisms may later become material that will burn and release the stored energy as heat. Also, bodies of dead organisms may be preserved for very long periods of time, and later be used as fossil fuels.
Many marine organisms use CO2 that has been dissolved by seawater to produce carbonates, principally calcium carbonate which later becomes stored as limestone. The CO2 from this may be stored for millions or billions of years before the limestone is exposed to conditions that decompose it.
The absorption of CO2 by water, and the use of some of this dissolved CO2 by marine organisms to produce carbonates, make the oceans a substantial buffer for CO2. However, when water gets warmer it can dissolve less CO2, which reduces its buffering ability against warming.
Positive and Negative Feedback
Buffers, which oppose the effect of heating, are a form of “negative feedback”. There are other processes that accelerate the warming or cooling. These provide positive feedback. One positive feedback effect is the melting of ice. Less ice means less reflection of the sun’s rays, increasing the amount of warming. The warming of water, which causes more evaporation and cooling of the water, and creation of more clouds that block the sun’s rays, is a double whammy negative feedback. However, when water is warmed it releases some of its dissolved CO2 and methane into the atmosphere, and also increases evaporation. Since the extra CO2, methane and water vapour, are greenhouse gases, this is positive feedback. Melting ice, in polar regions, glaciers, etc., cools the seawater, but because the cooler fresh water is lighter than the salty water below, it stays on the surface and slightly increases the amount of CO2 that the sea can absorb.
When permafrost thaws on land in arctic regions it releases CO2. Warming of hydrated methane on the sea bed in arctic waters releases methane. Both of these processes are positive feedback.
At present, positive feedback prevails, so warming proceeds. But the buffering effects of the oceans and the ice are slowing the increase of the temperature of the air at ground level. All this just illustrates the complexity of warming.
Evidence of Warming Occurring now
Measurements and other observed phenomena confirm that global warming has been occurring for some decades. Temperatures are increasing in both surface and deep levels of the oceans, in some levels of the atmosphere, in the ground up to a depth of about 50m, and in the ice in Antarctica and Greenland. During the past fifty years the global average temperatures have increased in step with the increased in greenhouse gases (with allowance being made for changes in air pollution). Almost all glaciers on Earth are melting and the amount of ice on mountaintops is decreasing. Species on land and in the sea are migrating towards the poles. On land they are also migrating to higher altitudes. Some species that cannot migrate quickly, such as some species of trees, are beginning to die out.
Weather and Climate
Weather is the local short-term pattern of
– wind strength and direction,
– and humidity.
In most places, the weather is continually changing by a small amount. Extreme weather conditions occur when the different forces that influence the weather happen to reinforce each other. The energy that is released when water vapour high in the atmosphere condenses to water causes strong wind and rainstorms. Warm surface waters in the ocean can start strong air currents to circulate. Higher temperatures increase the energy in these systems, making the storms, on average, more powerful and sometimes more frequent. Moister air at the same time increases the intensity.
Every weather event is the consequence of all the meteorological conditions preceding it. While global warming has affected the meteorological conditions, we cannot say what the weather would have been like had there been no warming. But the probability of greater extremes is higher when temperatures are higher.
Climate is the regional pattern of weather that is approximately repeated over a period of many years. It may be consistent from year to year or may have more than one kind of weather, e.g., years of drought and also years of rainfall.
Processes of Change
As discussed in the section on global warming, changes in temperature cause changes in winds, ocean currents, and the storage of heat and other forms of energy. All these are part of complex systems that affect weather and climate. Some of the major systems that affect climate are the Hadley circulation, the El Niño Southern Oscillation (ENSO), monsoons, the Gulf Stream and the Pacific Decadal Oscillation (PDO).
The Hadley circulation operates right around the earth in the tropics, moving north and south following the seasons. In equatorial regions, hot air rises and is then pushed towards the poles, at the same time becoming cooler and heavier. It then moves down to the surface, and then is drawn back to the area of low atmospheric pressure in the equatorial region, to repeat the circulation. This process increases the likelihood of rain in tropical zones and of deserts in the areas where the air descends to the surface (all subject to winds and the location of mountains and oceans). These areas of rain and desert move further from the equator when global temperatures rise, so global warming and cooling affect the location of tropical lushness and the major deserts. This occurs in two belts that extend from approximately 50o to 30o north and south of the equator. During the past thirty years the Hadley cycle has widened, moving these belts by about 150 kilometres to the north and to the south.
There are similar systems, two around the polar regions and two between the Hadley and the polar circulations. Warming in the polar areas widens the range of the polar circulation in a similar way to warming of the Hadley cycle, and also brings polar temperatures to regions further from the poles, which is now happening in northern regions of Europe, Asia and North America.
ENSO is not exactly an oscillation. It relates to two conditions that can appear, largely unpredictably, in the South Pacific Ocean. The conditions are known as El Niño and La Niña. ENSO is caused by the complex patterns of the Humboldt ocean current, which circulates the South Pacific Ocean. The current is affected by the water temperatures and salinity in tropical and polar regions and by the winds associated with the currents in these areas.
El Niño is the result of warmer waters, and the associated warmer air and lower atmospheric pressure, along the west coast of South America. This causes warmer drier seasons in Australia, South East Asia, and eastern Antarctica. It causes wetter seasons in western South America and has more complex effects in eastern Africa and North America.
La Niña, which results from colder currents along the west of South America, causes more cyclone activity in the Pacific ocean and wetter seasons in Australia. The cold surface water during La Niña causes more absorption of solar energy by the ocean, which reduces average global land surface temperatures. During 2008 and 2011, La Niña lowered the global average temperatures below the previous years, but they were still warmer than any previous La Niña. Sea levels also are lowered by La Niña events because heavier rainfall transfers water from the oceans to the land. After the end of each La Niña the pre-La Niña sea levels and trends in global temperature are restored. In contrast to these effects, a “super El Niño” in 1998 caused unusually high global temperatures, with succeeding years being cooled by a return to La Niña. (Nevertheless, the successive 15 hottest years on record have all occurred since 1998.)
Monsoons are caused by differences in the temperatures of the sea and adjoining lands. Many countries depend on them for the rainfall they bring. They are already being affected by global warming.
The Gulf Stream circulates around the north Atlantic Ocean. The southern section, starting from Florida, crosses the Atlantic to southern Europe and then flows north, warming the countries along the west coast of Europe. It then becomes known as the North Atlantic Drift as it moves into Arctic Ocean, and is turned westward by the obstructing land masses and Arctic Ocean ice. On reaching North America, it turns southward along the coast, cooling the eastern regions of Canada and the USA. It is speculated that the continued reduction of ice in the Arctic Ocean will disrupt the circulation. This could mean a reduction in the cooling of the east coast of North America, in addition to any other effects of global warming. In the meantime, the gulf stream along the west coast of Europe is getting warmer
The Pacific Decadal Oscillation (PDO) is associated with ocean currents n the North Pacific Ocean, mainly in the tropical region. In one phase is has a global warming effect and in the other phase a global cooling effect. It changes from one phase to the other every 20 to 30 years. The cause of the PDO is not understood. At present it is in a cooling phase.
Temperature differences between equatorial and polar regions are a major driving factor of many global climatic conditions. These differences have been decreasing over the past decade because the temperatures are increasing more in the polar areas than in the tropics. This is affecting all of the major systems, and also the weather.
Another process affecting climate is the change in the buffer systems. Continual reduction of the amount of ice (the ice buffer) will speed up warming. Continued warming of the oceans will reduce, and eventually reverse its absorption of CO2. Warming may cause more lush vegetation that would absorb both heat and CO2. This could be negative feedback. But the heat and the CO2 could then be returned the environment by bushfires on an unprecedented scale.
Any model that tries to predict global heating, global warming or climate change will be only as good as the completeness and the accuracy of its details. Both of these requirements depend on the amount of fine detail is available of all the climate system. The extensive climate measurements that continue to be made across the globe over the past decade or so, and also the geological evidence, have been done rigorously. All known influences that might have made the models inaccurate or not representative of the true situation have been taken into account. Recent models of the climate system have produced close approximate representations of the actual broad trends. (The published forecasts are more cautious than the calculations predict.) So if there are any unknown factors influencing global climate their effects are very small.
There are important known factors whose behaviour cannot be predicted but will effect global climates over the next few decades. One is whether the emissions of radiation from the sun will continue to decrease or will start increasing. Another is when the Pacific Decadal Oscillation will switch from its present cooling phase to its warming phase. We can do nothing about the sun, and possibly nothing about the PDO. Various “engineered” interventions that might block out incoming heat from the sun or reduce the amount of greenhouse gases in the atmosphere have been proposed. But their feasibility and effectiveness are uncertain and their side effects could be dire.
Another unpredictable critical factor is how long it will be before each tipping point will occur in the global systems. This, and global warming generally, will depend on what will be done in the various countries to either act upon or ignore the situation. Global warming began when the amount of carbon dioxide in the atmosphere was much lower than it is now. Carbon dioxide lasts in the atmosphere for an average of 100 years, so instead of continuing to emit increasing amounts we should be causing continuing net reductions.
The devastating consequences of global warming are becoming more and more obvious. It is already too late to stop them becoming much more devastating. Any action taken to reduce emissions will slow the rate of increase, but only drastic action will hold or reduce the temperature. Each government has its own policy position on the matter, based on its particular beliefs and priorities, and on those of its citizens. Governments and individuals often choose instant gratification, even when they know that it will cause future harm.
I think the future looks very bad.