This is a quick summary of global warming and climate change I prepared to help someone with their school project.
What is Climate Change & Global Warming
Climate change refers to any change of the climate including getting wetter or more wind. The world’s climate is constantly changing. Likewise, “Global warming” refers to one aspect of climate change: periods of increasing temperature. So there have been many periods of global warming. It has warmed since the last ice age, it has warmed since the little ice age (in 19th century). But in the last 19 years the satellites show no significant warming. And indeed in 2017 we saw huge global cooling as we came out of an El Nino. So “global warming ” is scientifically a very meaningless term without specifying the period you are referring to.
Whilst “Global warming” can refer to any period during which the earth has seen warming, it’s main use now, tends to be in the political arena where it is used to refer to the 20th century warming and the POLITICAL implication (which is not scientifically valid) that this “unprecedented” warming was caused by rising levels of CO2 and more specifically that this change will continue. However only a small fraction of the warming can be attributed directly to rising CO2, and most of the proposed warming is due to other feedback effects. These are highly speculative and at best unproven.
However, it is generally agreed the average temperature of the earth likely warmed in the 20th century, but that was a period when we came out of what was called the “little ice-age”. There is good science to suggest a fraction of the warming was due to a rise in CO2.
CO2 is a greenhouse gas, because it strongly absorbs and emits infra-red radiation (IR). As such, it tends to block IR from the surface which is at one temperature and emit IR at the temperature of the surrounding atmosphere and because the atmosphere gets cooler as we move up from the surface, more CO2 tends to block more IR from the surface and emit it from higher in the atmosphere at a colder temperature. So, the average temperature of the IR reduces, which means that less heat is emitted to space. And because less heat is emitted, the average surface temperature increases. However, this effect is small amounting to only a 1C increase for a doubling the amount of CO2 in the atmosphere.
Climate Change & Global Warming in context
However, there are many other things that cause temperature to change from the amount of cloud, to volcanos to changes in ocean currents. As a result the world’s temperature varies naturally.
But not only temperature changes. Climate change refers to any change of the climate including getting wetter or more wind. The world’s climate is constantly change. So, “Global warming” refers to just one aspect of climate change.
But the earth’s climate is constantly changing and so there have been many periods of global warming. It has warmed since the last ice age, it warmed since the little ice age (19th century). But in the last 19 years the satellites show no significant warming. And indeed in 2017 we saw huge global cooling as we came out of an El Nino.
But whilst “Global warming” can refer to any period during which the earth has seen warming, in the popular press and less respected areas of academia, it is now used in a political way to refer to the 20th century warming to suggest it was caused by rising levels of CO2 and more specifically that this change will continue. However only a small fraction of the warming can be attributed directly to rising CO2, and most of the proposed warming is due to feedback effects which are highly speculative and unproven.
It is generally agreed we warmed in the 20th century by about 0.75C, but that was a period when we came out of what was called the “little ice-age” so it started “unusually” cold. But there is good science to suggest a fraction of the warming was due to a rise in CO2. However, the longest temperature record from Central England also shows several similar scale warming periods in the last 350 years. Indeed the warming from 1690 to 1730 of about 2C was larger than the 20th century warming.
As no one attributes the 1690-1730 warming to CO2 and instead we assume that it and the other similar scale warming periods are due to “natural variation”, we know there is significant natural variation such that all the warming in the 20th century could be explained by natural variation.
On the other hand, ice-core records show an increase in CO2 at the time when ice-ages end. Many have taken this to suggest that there is some form of “positive feedback” that increases the small amount of warming that science predicts rising CO2 will cause. In other words, if CO2 directly caused 1C warming, they are suggesting there are other “effects” that must cause much more warming. However, there are also problems with this idea because CO2 lags the rise in temperature in the ice-core record – so rising CO2 appears to be caused by Temperature. However, we cannot be absolutely certain that air bubbles do not move very slowly through the ice which means cause and effect is hard to determine. Also, if there were massive positive feedbacks, why would the relatively sudden rise in temperature coming out of the ice-age stop? Surely if “global warming” could cause catastrophic warming today, then surely it would have happened when we warmed after the last ice-age. Something appears to make our present inter-glacial period relatively stable preventing further warming.
All we can say honestly
All that we can really say honestly, is that we still do not know how the climate works, and there is a huge amount of uncertainty. So, the only real test of whether rising CO2 (with positive feedbacks) would lead to massive warming is whether models predict what is happening in the climate. However, whilst the IPCC using this theory predicted at least 0.14C rise in temperature per decade, this did not occur in any of the temperature measurements predicted to rise. Indeed, the satellite temperature record shows no significant warming for 19 years. And note, the satellite measurement was introduced at great expense because of the known problems with surface based measurements. (E.g. there is no measurements from central Africa or central S.America and much of the sea area is unmeasured).
So, (unless we see a massive rise in temperature soon), the models predicting temperature rise now appear to be invalid. In other words, the speculation that there are positive feedbacks has not proven to be correct.
Why is Global warming called a hoax
Because of the difference between the serious scientific uncertainty and the popular certainty and lack of scientific rigour, many people call global warming a “hoax”. This is not to deny that the earth warms and cools regularly, because that would obviously be scientifically invalid. Instead it is a criticism of those that pick out just one such period of warming and suggest that this one is special and means the earth will continue warming. It is also a criticism of the lack of scientific rigour of many academics and researchers who fail to acknowledge that the 19 years without significant warming in the satellite record is strong evidence that their theory is invalid. It is certainly not proof in “global warming”!
It is also criticism of those like NASA who are constantly changing the data from their ground based measurements so as to suggest warming where there has been none. For example, all the warming since 1940 in the NASA temperature record is due to their adjustment of the data. So to suggest this adjusted data “proves” global warming is politically inspired non-science.
Is warming really a problem?
Throughout the world today, more people die from cold than heat (according to an article in the doctors magazine the Lancet). The figure in the UK is around 37,000 extra winter deaths each year and even in hot places like India there are more winter deaths. In the UK, winter deaths reduce in mild winters. We also know that many crops have to be grown in greenhouses in higher temperatures. So, it is not surprising that we expect to get huge benefits from a small increase in temperature. For example, northern countries like Scotland could do particularly well out of any warming because it would dramatically increase the growing season.
But at around 2C many academics postulate that the scale of predicted harm becomes significant, such that they predict that there will be net harm if the temperature rose higher. This is a difficult figure to quantify and being subjective the calculations are likely to be affected by the individuals views. But in effect the change is as if everyone moved a few hundred miles closer the equator. In the UK, it is like moving to Spain – and as many UK residents retire to Spain – they clearly see the higher temperature as beneficial. No one argues that at some temperature the bet harm will exceed the net benefits, but again, no one really knows whether it is 2C or 4C or indeed 6C warmer. All we do know, is that the world has been a lot warmer in the past and e.g. in the carboniferous with higher levels fo CO2, the world’s plants and animals seems to have flourished.
Is CO2 a problem on its own
The other thing worth mentioning is that rising CO2 also has an effect. As a plant food it is literally causing a “greening of the planet” particularly in dry areas. On the other hand, a rise in CO2 will change the PH of the oceans REDUCING the alkalinity of the water slightly (approximately the same scale as occurs naturally between day and night). Moreover, in periods such as the carboniferous when CO2 levels were much higher than today, there seems to have been no ill effects on plant or animal life.