This current article started out as a simple article about the time lag (or response time) between a change in CO2 level and when the warming takes place. The warmist theory indicates that it takes decades or centuries for the full effects of CO2 to be felt. This is in stark contrast to all other atmospheric effects that show a response on the order of a few months for the full effects to be felt.
The article grew long enough that it will now be a two part article. The first will cover the time lag of the Earth for different types of changes. The second part will discuss the theory that warmists use to support the claim that it will be a hundreds or thousands of years before the full effects are felt.
This is one of the least discussed aspects of global warming, but it is absolutely critical for future projections of warming. If there is little to no time lag, then the full effects of current CO2 emissions are already being felt. If the lag is 50 years, then we are only starting to feel the effects of the emissions from 1960 when the CO2 level was still around 320 ppm. The importance of understanding how quickly the climate responds is critical to future projections.
Not surprisingly the warmists relentlessly claim that the time lag is long, often decades or centuries, but sometimes even longer. This belief shows up in multitudes of comments that most of the warming has yet to happen, but we are always assured that it will happen. The statement “yet to happen” is a vague statement, but one that shows the belief that the time lag is long. Implicit in that statement is the belief that the time lag is greater than 50 years which is when CO2 levels started to show significant increase.
So what I have done is looked at specific events and determine the time lag for the effects to show up in the Earth’s climate. Fortunately there are many other events aside from CO2 that influence the Earth’s temperature and it is easy to determine the typical time lag from these events.
The first event is one that many people has heard of, but probably not considered the time lag nature of the event. It is the commonly quoted paper that discusses the impact of the airline grounding after September 11th, 2001. In the days that followed there was no commercial airline traffic in the United States for the nights of September 11-13. Traffic resumed on September 14th. The paper (Travis, 2004) claims that the difference between night and daytime temperature range (DTR) increased by more than 1 °C as a result of the decrease in contrails.
If this study is correct then the time that it takes for radiative heat transfer effects is very short. In fact the period for the impact to be felt is less than 24 hours. The paper claims that by the morning of the 12th there had already been a statistically significant change in DTR as a result of reduced contrails. According to the paper the low temperatures for the morning of the 12-14th were statistically different as a result of the reduced contrails.
In addition the paper claims that the resumption of air traffic on the morning of the 14th caused an almost immediate reversal in the DTR back to the more normal levels. This claim is most commonly shown by the following chart.
Now I am aware that other papers have made a strong case that the Travis paper is flawed, but even the Hong paper supports the idea that quick changes in cloud cover cause quick changes in DTR. The basis for both papers is that clouds (natural or contrail) cause immediate changes in the radiative heat transfer (RHT) of the specific location. Nowhere in either paper is there an indication that radiative effects take much time to be felt. Both papers strongly make the case that the effects of RHT are almost immediate.
Another event that attracts media attention is the El Nino / La Nina (ENSO) cycle in the equatorial portion of the Pacific Ocean. These events are defined as a warming or cooling of that region of the ocean. The effects of the ENSO are felt in the period about 4-6 months after the ocean temperature started to change. The effect is either a warming of the atmosphere or a cooling of the atmosphere above the ocean depending on the phase of the ENSO. In this situation the entire average temperature of the tropical atmosphere is affected within that 4-6 month period of time by a change in the surface temperature of the ocean.
While the time delay is greater for this case than the first, it is a much larger change. Even with the larger scale it is only a matter of months before the full effects are felt. The effects of the El Nino over 2009-2010 was replaced by the effects of the La Nina that developed during the last half of 2010 and significant atmosphere was showing that cooling by December. This is VERY strong proof that the the time lag for the climate is a matter of months and not decades.
Another event that happens every year is the seasonal changes that are caused by changes in the energy from the Sun to different parts of the Earth. These changes have a a time lag of no more than a month or two. The highest/lowest energy days are the solstices and the month after tends to the the warmest or coldest. After that the changing levels of solar energy causes the temperature trends to reverse. The seasons that take place every year tell us that it doesn’t take years for changes to be felt. Once again the real world evidence is that the time lag is months and not decades.
Perhaps the strongest case for an immediate effect of a change to the Earth’s atmosphere is the eruption of Mt. Pinatubo in June of 1991. This was a very large volcanic eruption that resulted in large amounts of ash and sulfur dioxide into the atmosphere. The impact to the global temperatures was felt within months. The primary cause of this was the ash in the atmosphere reflected more energy from the Sun away from the Earth. The result was cooling. The average temperature of the Earth dropped 0.5 °C a year after the eruption.
The stratospheric cloud of sulfur dioxide lasted for 3 years. While the cloud existed it provided a cooling effect. As it started to dissipate so did the cooling it provided. As it disappeared after three years, the Earth’s temperature had recovered. As the ash in the atmosphere decreased, so did the effects of the ash on the Earth’s temperature. Both in the start and end of the effect there was no significant time lag. This is a perfect example of an atmospheric only event that caused the Earth’s climate to change while it persisted, but the moment it faded so did the effect it provided.
The evidence from these events is very clear. The Earth responds to changes in a matter of months. Since CO2 levels should be considered an event, the response of the Earth is only a few months behind the global CO2 levels. That would mean that the full effect of CO2 today is based on the current CO2 levels. For all intents and purposes that is an immediate response as CO2 levels change little over the course of a few months.
In no case is there evidence of time lags taking more than a few months to impact the Earth’s climate system. The closest would be the glacial/interglacial transition. Those events take place over thousands of years, but melting ice sheets that cover large portions of the Northern Hemisphere takes thousands of years so that is a very different situation.
What makes more sense? That a change in RHT would be quickly felt or slowly felt?
It should be no surprise that RHT has a quick impact. For all intents and purposes RHT is instantaneous within the atmosphere. When a cloud blocks the sun on a cool day it is felt right away. Walking into the shade on a hot summer day makes a difference just as quickly. The temperature of the air remains that same in both cases, but the change in heat transfer has no noticeable delay. There is no difference for the effect of CO2 in the atmosphere. Any warming by additional CO2 will have an almost immediate impact on the amount of heat transferred. This will result in warming almost as quickly.
One reason the atmosphere responds quickly is because it is very sensitive to changes in energy. It warms up and cools down quickly. Nothing else is as sensitive as the atmosphere when it comes changes in energy. That is because it takes very little energy to cause a temperature change in the atmosphere. Water takes much more energy to warm up. Warming up 1 m3 of sea water takes ~3600 times more energy than warming up 1 m3 of air. So the same energy that would warm up the air by 1 °C would warm up the same volume of water by 0.0003 °C. This is why the atmosphere theoretically should respond quickly to changes in energy. So the examples in the Earth’s climate and the theory match up. The Earth’s atmosphere should and does respond quickly to changes in energy.
If there is very short time lag between a change in CO2 level and the full impact from being realized, then we are currently experiencing the entire impact of the past CO2 emissions. There is no additional warming that will happen in the future, what we have now is all the warming that will happen for the CO2 levels that currently exist.
That idea is anathema to the warmists that believe in global warming. They cannot accept that much greater impacts will not be felt in the future as a result of the current CO2 level. The reasons are simple. There is no future crisis to avert if there is not much greater warming in the future and that means there is no critical need to reduce CO2 emissions.
So in order to create a method for future warming to happen they have created another theory that goes by the name of thermal inertia. Inertia implies that once something gets started it is hard to stop because it is already in motion. The theory of thermal inertia is one of the most important aspects of global warming and it is also one of the least discussed.
In the next part I will delve more into this theory that claims even if CO2 emissions stopped now, the Earth would keep warming for hundreds or even thousands of years, even though the Earth is not showing evidence of significant warming yet. That is why the theory of thermal inertia is so very critical to understanding the warmists view of global warming.