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Climate meme debunked as the ‘tropospheric hot spot’ is found

Posted on 11 June 2015 by Guest Author

This is a re-post from The Conversation by Steve Sherwood, UNSW Australia

Before climate sceptics got excited about the “hiatus” or slowdown in global surface warming during the past 15 years or so, they were fond of discussing the “missing tropospheric hotspot” – the alleged lack of anticipated temperature increase in the tropical upper troposphere (roughly 5-15 km altitude).

Both the “hiatus” and the “missing hot spot” have been interesting research problems, because models seemed like they might be missing something important.

There have been significant advances on both problems in the past year. And the new results do not offer much hope that scientists are fundamentally mistaken about global warming.

The “hiatus” has been addressed by a veritable avalanche of recent studies, as reported in articles on The Conversation (such as here and here). These studies collectively show that the warming slowdown has been the temporary result of a regularly recurring change in ocean circulation – essentially, a bump in the road towards a warmer planet. The phenomenon has no evident link to global warming or the physical principles that connect it to greenhouse gases.

Hitting the spot

But what about the “missing hot spot”? In this case, part of the atmosphere has reportedly warmed little, in spite of predictions that it should warm significantly faster than the surface. This would seem highly relevant to the question of whether humans are causing climate change, although in fact, the warming maximum should happen equally whether warming is natural or human-induced. Still, the seeming lack of such warming is an important puzzle for atmospheric scientists.

I wrote here in 2011 that recent (at the time) satellite studies were coming closer to showing the expected warming, but were still not all the way there. Some analyses of the data seemed to show it but were not completely convincing. Now, three newer papers make it look very much like the tropical atmosphere has indeed been warming as expected all along.

First, a 2013 paper, featuring a new analysis of radiosonde (weather balloon) data showed increased warming in the upper troposphere. This analysis, which used weather forecasts to help identify artificial changes in the balloon data (such as those due to undocumented changes to instruments), also came up with a reassuringly realistic pattern of warming compared with earlier efforts.

My colleague Nidhi Nishant and I have now analysed the radiosonde data yet again, and we found a tropical warming profile even closer to that expected. The fastest warming was at an altitude of about 12 km, and averaged 0.25C per decade – much faster than at the surface (0.14C per decade).

This means that the troposphere is warming around 70-80% faster than the surface. So, far from being absent, this tropospheric warming is at least as strong as predicted by the average climate model, which predicted that the troposphere would heat 64% faster than the surface.

Moreover, our data show that the tropical troposphere has warmed at a more or less constant rate since widespread balloon launches began in 1958, which is a bit puzzling given the ocean-surface hiatus since 2000 or so.

More evidence

This result comes hot on the heels of a new University of Washington study which overcomes one of the key obstacles to obtaining an accurate satellite-based record of atmospheric warming. The problem is that temperatures vary during the day, and when a new satellite is launched (which happens every few years), it observes the Earth at an earlier time of day than the old one (since after launch, each satellite orbit begins to decay toward later times of day).

This means that over time, if you don’t know the daily cycle of temperature very accurately over the whole planet, you are going to get an errors in the long-term warming trend when you piece the different satellite records together. The University of Washington group has come up with a way of estimating this temperature cycle from the satellite data themselves while at the same time accounting for other effects such as calibration changes.

The result is that they now find mid-to-upper tropospheric warming that is just as strong as predicted by models, in line with both of the new radiosonde studies. The troposphere was warming all along – it’s just that the warming is very hard to see when other things are happening to the instruments over time.

One remaining puzzle is that the radiosonde data do not show a “hiatus” in atmospheric warming, but the satellite data do. Another is that the surface warming rate over oceans has been somewhat weaker than predicted by most climate models, even going back well before the “hiatus.”

This could be due to the models being too sensitive, but would be more easily explained by the existence of some influence on climate that has up until now been partly offsetting the greenhouse effect, and has not been properly accounted for. Thus climate scientists still have important puzzles to solve — but it looks like the “missing hot spot” has finally been found.

Steve Sherwood is Director, Climate Change Research Centre at UNSW Australia.

This article was originally published on The Conversation. Read the original article.

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Comments 1 to 4:

  1. "recurring change in ocean circulation – essentially, a bump in the road towards a warmer planet." How does ocean circulation change the energy budget of the planet? If there was energy lost due to theses bumps, where did it go and how will it come back?

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  2. topal,

    The reference was to a "hiatus" of the global average surface temperature. And the global average surface temeprature is not the energy budget of the planet. The energy budget has many accounts for energy to be stored in with the biggest being in the ocean depths due to ocean circulation patterns.

    A major ocean circulation pattern that can take energy into or deliver energy out of the ocean account is the El Nino/La Nina. When the condition is El Nino the ocean account releases heat to the surface creating a temporary condition of global average surface temeprature that is higher than the ENSO neutral condition. When the condition is La Nina the ocean account takes in heat from the air at its surface creating a temporary condition of global average surface temeprature that is lower than the ENSO neutral condition.

    Te history of two major measurements related to the ENSO are the NOAA Reported ONI here and the Australian reported SOI here. Reviewing the pattern it is clear that the SOI El Nino indication comes a few months before the ocean surface temperature reaches the threshhold for declaring an El Nino eevent to be occurring. Both sources provide detailed explanations of how the values are determined and how they relate to the ENSO.

    When you look at 1998 in particular you see just how significant the 1997/98 El Nino condition was. You will also see how significant the La Nina was before and after it. When you look at the temperature records of that period using the SkS Temeprature Trends here, whatever one you choose even the satellite ones, there is a trough before and after the massive peak of 1998. The random sort of cyclical ENSO influence on the surface temperature is clearly the best explanation for the wide swings of global average surface temperature.

    The signicant troughs or lower global average surface temperatures before and after 1998 are often ignored or 'deliberately missed' by people trying to claim that it hasn't warmed since 1998. And of course it becomes obvious why they pick 1998, or any of the other more recent peaks in the varying global average surface temperature record.

    Reviewing the ONI and SOI since that time shows that there have been more La Nina than El Nino conditions, and the El Nino conditions have not been as significant as the 1997/98 event. This mean that the global average surface temperature influence of the ENSO has been more of a cooling influence through this period. And the fact that the global average surface temperature in 2014 was warmer than 1998 even though the ENSO was neutral is an indication that significant warming has occured since 1998.

    Of course there are many other random and cyclical factors that have temporary effects on the global average surface temperature. It is just that the ENSO is clearly a significant one.

    I hope hat helps you understand why the effect of increased CO2 has continued to occur, and why reviewing the global average surface temperature values through a short time period like the past 17 years is not a robust way of evaluating what is going on. A recent report by NOAA discussed here actually makes a minor correction of the surface temperature data and finds that the minor correction significatly changes the recent trend of the global average surface temperature.

    The understanding of what is going on continues to improve. And the evidence that the warming effect of increased CO2 is occurring as expected is becomeing even more robust.

    p.s. The Free Course offered in the link at the top of the right hand side of the SkS webpage will help you better understand this far more than my comment. I have not completed the course, I have only been able to get through about half of it to date.

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  3.   When the condition is El Nino the ocean account releases heat to the surface creating a temporary condition of global average surface temeprature that is higher than the ENSO neutral condition.

    How does the ocean know it is El Nino and what is the process that heats the surface (of the ocean?)?

    When the condition is La Nina the ocean account takes in heat from the air at its surface creating a temporary condition of global average surface temeprature that is lower than the ENSO neutral condition.

    When the ocean takes in heat from the air, I'd guess that the surface temperature of the ocean would increase (and the air temperature decrease). But how is heat transfered from the air to the water, given the huge difference in heat capacity between water and air?

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    Moderator Response:

    [Rob P] See the SkS post How increasing carbon dioxide heats the ocean. You make a good point about the differing heat capacities of water and air. Not many people intuitively grasp how unphysical it is for the oceans to be warmed by the transfer of heat from the atmosphere given the enormous difference in heat capacity. Then there's that whole 'laws of thermodynamics' thing too.

    Long story short; during El Nino more warm water is at the ocean surface (especially the tropical Pacific) and this leads to the anomalous transfer of heat from the ocean to the atmosphere - hence warmer-than-normal global surface temperatures. 

  4. Topal,

    In addition to what Rob P has provided, any warm surface will warm cooler air that passes by it. And any cool surface will cool warmer air that is passing by it. That is the basic physics expectation of mechanical heat transfer systems. So when a wind blows air across a water surface some heat transfer will occur. This is what makes the influence of an El Nino larger than just the local warming of the ocean surface. The longer the condition occurs, and the more significant the condition is, the more warming of air can occur compared to an ENSO neutral case increasing the measured surface temperature in other areas.

    Rob P is correct that another effect is the change of the rate of heat loss by radiation of heat energy from the surface. So when the surface of the tropical Pacific is cooler (La Nina) more of the solar energy it absorbs stays in it.

    So technically it was incomplete to say that the ocean takes in the heat from the air. A cooler ocean surface is also releasing heat energy to the atmosphere at a lower rate than a warm ocean surface. And that radiant heat energy can be picked up by CO2. And if winds bring cooler (less energetic) CO2 over the ocean then that cooler CO2 will become warmer (more energetic).

    However, this technicality does not alter the fact that there is an obvious strong correlation between the variation of the ENSO and fluctuations of the global average surface temperature. Therefore, regardless of the specifics of the mechanism of incluence of the ENSO on global average surface temperatures it is obvious that the El Nino/La Nina influence is a significant factor and is a major part of the explanation that there has been no real 'hiatus' in global average surface temperature increase since 1998.

    Adjusting that variation of the rate of energy emissions from the surface of the tropical Pacific to an ENSO neutral ocean surface condition, including the adjustment of the effects beyond the tropical Pacific, would be the proper way to evaluate the trend of the global average surface temperature due to increased CO2.

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