Large changes in tropical rainfall expected due to greenhouse gas emissions

A new Met Office study has found that, if global greenhouse gas emissions are not reduced, we are likely to see large changes to the rainfall in tropical countries.

Scientists found that the size of these changes will be strongly determined by the total amount of greenhouse gases that are emitted.

Many people in tropical regions, which contain some of the least developed countries in the world, are already exceptionally vulnerable to variations in how much and how frequently it rains.  Any large, long-term changes to rainfall amounts due to climate change could worsen this vulnerability, and test the ability of societies and wildlife to adapt to potentially unprecedented conditions.

Climate simulations of tropical land rainfall change and global temperature change over the 21st century under four different greenhouse gas emissions scenarios.

Climate simulations of tropical land rainfall change and global temperature change over the 21st century under four different greenhouse gas emissions scenarios.

 

To investigate possible changes in future rainfall patterns, Met Office scientists used a large number of climate change simulations of the 21st century, produced by research institutes across the world.  All simulations run with high greenhouse gas emissions produced large changes in rainfall patterns across substantial areas of tropical land by the end of the century.  On average around one quarter of all tropical land was affected – an area twice the size of Brazil. Simulations run with lower greenhouse gas emissions showed much smaller areas of land with large rainfall changes.

Which regions are most vulnerable to rainfall change?

Analysis of future climate simulations shows that under high greenhouse gas emissions, large rainfall changes are expected to occur over an even larger area of dry land than was affected during the Sahel drought. Of course the impacts of such changes would be heavily dependent on the resilience of the particular countries affected.

The long-term drought in the Sahel region of West Africa brought famine to hundreds of thousands of people and huge disruption to millions more in the 1970s and 80s. Although not clearly linked to greenhouse gas emissions, the Sahel drought provides a yardstick for the potential impacts of future climate change.

When and why will these changes happen?

Rainfall changes in tropical countries are expected by the end of the 21st century due to climate change affecting a number of the processes which determine where and how much it rains in different parts of the tropics. One of these is the pattern of surface temperatures across the tropical oceans. As rainfall tends to occur over the warmest parts of the oceans, any changes to these patterns can cause large changes to the regions where it rains – this is what happens during an El Niño event.

Exactly where will changes occur?

Exactly which countries will be affected by these future rainfall changes is much less certain, as climate simulations disagree on where the changes will occur. Regions thought to be most at risk of large decreases include southern Africa and Central America, while India and East Africa are among those most likely to experience large increases. However it should be emphasised that the location of changes is much less consistent among climate simulations than the fact that large changes occur.

This entry was posted in Met Office News and tagged , , , , , , , , . Bookmark the permalink.

19 Responses to Large changes in tropical rainfall expected due to greenhouse gas emissions

  1. jbenton2013 says:

    Yet more unreliable climate model output presented as fact by the now discredited Met Office.

    Even if this were true (of which there is no credible proof) there is no mention of the fact that additional rainfall in many of the equatorial regions would be beneficial and contribute to the greening of dry and desert areas.

    This sounds like something Peter Stott would have dreamt up. How’s the data to support your claims in the media that the Somerset flooding was caused by AGW coming along Peter.

    • Please could you direct us to the media stories about Somerset flooding so we can properly address your comments.
      Thanks
      Helen

      • jbenton2013 says:

        Peter Stott was widely quoted in several media stories, particularly on the 9th and 10th January 2014 when that other great climate scientist David Cameron linked the Somerset flooding to climate change, while wading through the water for a photo op on the BBC news.

        I was first aware of the Peter Stott comments in the BBC news article but he was also widely quoted in the printed media eg the Telegraph article on the 10th January 2014.

      • Thanks for this. Please could you highlight exactly where Peter spoke directly about the link between Somerset flooding and climate change.

      • jbenton2013 says:

        I suggest you also look at the comments from your chief scientist Slingo in the BBC News article on the 9th February 2014 linking the Somerset flooding on climate change.

        Perhaps your chief scientist would like to disassociate herself from her earlier comments given we now know the reason for the Somerset flooding was very largely caused by negligence by the Environment Agency failing to dredge/maintain the man made drainage system.

    • carlgt1 says:

      Why do they even bother having comments here from anti-science conservative pseudo-intellectual? Peter Stott and the MO isn’t “discredited — only if you’re watching “news” from Rupert Murdoch……

  2. nuwurld says:

    Hi Helen.

    So, to condense,

    “Scientists found that the size of these changes will be strongly determined by the total amount of greenhouse gases that are emitted.”

    “Although not clearly linked to greenhouse gas emissions”

    “Exactly which countries will be affected by these future rainfall changes is much less certain, as climate simulations disagree on where the changes will occur. ”

    So in short, episodes of rainfall change in the past cannot be linked to greenhouse gases. But you are certain that larger areas (undefined) in the future will from time to time experience rainfall pattern changes and that will ‘definitely’ be due to greenhouse gas emissions.

    Sounds like ‘more funding is required’ to further this ‘junk science’, whilst avoiding the reality that the climate is always ‘naturally’ varying anyway.

    The Sahara was green and fertile several thousand years ago and progressively dried into the desert we know today. The inhabitants were forced to migrate to Egypt where the Nile brought regular fresh water from the African tropics. The Egyptians stored sufficient grain to survive several years of drought, but still natural variation caused these rains to fail and their civilisation collapsed. All without ‘greenhouse gases’. Mind you, some would still have blamed some unconnected aspect of human affairs!

    Good luck with the fictional narratives.

    • Large regional rainfall changes have occurred in the past in the tropics, and many of these are not thought to have been connected to greenhouse gases, particularly before the 20th century. However if the amount of greenhouse gases in the atmosphere continues to increase, this is expected to become the dominant influence on tropical rainfall change.

      As greenhouse gases concentrations increase, climate change is expected to bring large rainfall changes to a substantial proportion of tropical land. This is because climate change affects many of the processes that control the location and amount of rainfall in tropical regions, for example the temperature contrast between land and ocean. Exactly where these changes will be is currently less certain, but is an area of active research. We can say which areas are thought to be most at risk of large changes, and these include southern and east Africa, and India.

      • jbenton2013 says:

        Can you post the data and graphs to support your claims. Presumably the increase in CO2 from 280ppm to 398ppm over the past 80 years will clearly demonstrate there is a basis in empirical data supporting your claims.

      • nuwurld says:

        Hi again Helen,

        “Large regional rainfall changes have occurred in the past in the tropics, and many of these are not thought to have been connected to greenhouse gases, ”

        So the Earth within the solar system has ‘naturally’ in the past, exhibited significant ‘climate change’. But now, no natural variation can occur without the inclusion of ‘greenhouse gases’? These suddenly doing for the Earth what it always managed to do without them.

        Amazing! Thanks for that.

        Can you be more specific. Use of the phrase ‘climate change’ covers all possible variations. Surely what you mean by ‘climate change’ under any emission forecast is ‘global warming’, not just ‘any’ variation but those specifically that arise from warming beyond natural variability.

        ‘Climate change’ does indeed affect precipitation patterns but that is true if the world warms, or cools, or redistributes heat without affecting the global mean. And whether the cause is natural or not is obscured by your terminology as we can always guarantee variation somewhere. However, without proof you pin the tail on the GHG ‘donkey’. Effectively making asses of us all.

        Climate change (sign unspecified) is likely to cause changes in the ‘processes that control …..rainfall’ (perfectly true but it always has changed and always will), for example the ‘temperature contrast between land and ocean’ (again, sign unspecified). So you are pretty certain that some change will occur somewhere at some time and when it does, it will be due to ‘greenhouse gas’ emissions. I think you have covered all the options in obscure remarks. If anything happens anywhere then you will be shown to be correct.

        My apologies to the many scientists doing real research into global weather and climate who are railroaded by conflict of interest into having to agree with your agenda.

  3. HH Lamb showed that the Sahel drought, and indeed widespread drought across Asia, particularly India, was caused by global cooling, and particularly a much colder Arctic, in the 1960’s and 70’s.

    It is a pity that the CO2 obsessed Met Office now seems to have forgotten this accumulated knowledge.

    • carlgt1 says:

      Total BS — “global cooling” was a few crackpots in the 70’s — no scientific consensus at all. It’s a shame the MetOffice allows comments by anti-science idiot conservatives who think global warming is a hoax…..

      • DOHH!!

        http://unesdoc.unesco.org/images/0007/000748/074891eo.pdf

        Try pages 17-20, 44, and 48 for starters

        Lamb starts off by saying :
        “For the past 30 years the temperature of our planet has been steadily dropping”

        He goes on
        “The most serious effects, however,
        have probably been the long-continu¬
        ed droughts and deficient rainfalls in
        various parts of the world associated
        with shifts of the world’s anticyclone
        belts.”

        He was obviously another crank!!

      • nuwurld says:

        carlgt 1.
        It’s amusing when arrogant types come along and compromise themselves almost with every sentence.

        “Total BS — “global cooling” was a few crackpots in the 70’s — no scientific consensus at all.”

        Both the Pacific and Atlantic Oceans were in their negative temperature anomaly phases during the 60’s and 70’s.

        Easily checkable.

        Now that is a huge portion of the Earth’s surface with a negative temperature anomaly that had been warmer in the 40’s and 50’s. The Northwest Passage was open and sailable in 1903 but it certainly wasn’t in the 60’s and 70’s!

        “It’s a shame the MetOffice allows comments by anti-science idiot conservatives who think global warming is a hoax…..”

        Anthropological Global Warming IS A HOAX. There is no ‘think’ about it.

        The Roman Warm Period and the Medieval Warm Period have been shown by a consensus of literature to have been warmer than today’s ‘unprecedented’ temperatures (the Holocene Climatic Optimum was 4 to 8 thousand years ago with a progressive downward trend towards the next onset of glaciation). These warm periods were interspace by the Dark Ages Cold period and the Little Ice Age illustrating a strong natural periodicity in temperature. As we approached another great warming plateau after recovering from the LIA the ‘tax carbon’ police popped up and start ‘bleating’ about GHG back radiative nonsense, from an industry that has cost the western world trillions of dollars and pounds and is of no productive use in a world where billions live on the breadline. The corruption of academia by economic means that Eisenhower warned of has proven to be true at a fantastic cost, both monetarily and scientifically.

      • Carlgt, you display a frightening lack of knowledge if you consider HH Lamb a crackpot, you might want to clarify that.

  4. Lets see CO2 is heavier than air so will naturally fall to sea level where it will help pump extra water into the air, which looks as if it will mainly fall in the tropics and the concentration of poor countries in the tropics will make this extra rainfall problematic.
    Lots of broken toys in here, is someone’s mummy going to pick them up?

    • nuwurld says:

      Sorry, but you are going to have to be ‘much more specific’ to communicate here.

      CO2 ‘is’ heavier than air, as you suggested. But the measured vertical distribution tells us that diffusion and advective transport leaves only a few ppm difference between the surface layer and stratosphere. So in reality the ‘natural falling’ needs, and I openly invite, support.

      Secondly,

      “where it will help pump extra water into the air, ”

      From what physical process is this please?

    • nuwurld says:

      Michael,

      Perhaps it’s worth you checking ‘evaporative pan’ data, as this shows that less water evaporates these days than 50years ago. The overlying trend is downwards across the globe indicating a paradox with the ‘illusionary world of the climate alarmist’. Warm air can hold more water, and higher temperatures increase evaporation rates, but still less water evaporates as shown by thousands of parallel experiments across the Earth???

      Mmmmmm…..

Comments are closed.