Hotter Tropics and Higher Tropical Rainfall Totals. Reason for Concern or Merely Cyclical Variance?


In 2007, an article was published in Science and Development Network that shared data from the NASA Global Precipitation Climatology Project that “analyzed the global rainfall record from 1979 to the present.” It confirmed one thing that most scientists have long known – that absolute global rainfall amounts have remained fairly constant.

The discovery that was surprising was

that while there has been no overall global change, rainfall over oceans in tropical latitudes increased by five per cent over the period and decreased by one per cent over land.

What I also learned from the results is that

two-thirds of all rain globally falls in the tropics.

Perhaps a more relevant question raised in 2007 by the co-researcher of the study was:

What’s interesting is that if this kind of change in precipitation is happening with temperature change, what’s going to happen over the next 50 or 100 years?

The implication being that with forecasted global temperatures expected to continue to rise because of increasing levels of atmospheric gases, we will be in for some much more dramatic tropical weather extremes.

Just 1 year later (2008) from a study in the NYTimes: Expanding ‘Deserts,’ by Land and Sea and the picture gets a bit clearer – or not. We know that all of the “real” moisture action occurs around the Equator.

In fact, it is not uncommon for many places located near the equator to receive over 2800 mm (100 in) of precipitation a year! You can get this and other good explanations of the influence of the tropical heat, climate and rainfall from the following three sites: The Equator to the Subtropics; Climate and Rainfall; and Global Atmospheric Circulation. The information is somewhat repetitive but I think it is better to err with a bit too much than too little.

Back to the 2008 NYTimes article.

Scientists have long projected that areas north and south of the tropics will grow drier in a warming world.” But there will be a lot of consequences in the oceans, as well. According to the study, it is projected that “relatively plankton-free stretches of the Atlantic and Pacific Oceans around the tropics that typically cover about 20 percent of the global ocean surface have expanded about 15 percent since 1998.

From a previous post on the Amazon, it was shown how much nutrient passes from the river into the Atlantic Ocean. However, we might deduce that with rising equatorial-region temperatures, there will be diminishing plankton to feed on the nutrients and fewer fish to feed on the plankton. And this is just because of rising ocean temperatures and not over-fishing! The food change will become more and more challenged.

Yet, comments to the Times study also suggests caution in drawing sweeping conclusions from short-term data results. Dr. Held identifies numerous studies showing dramatic changes from

the retreat of the Arctic ice last summer, Greenland melt, trends in Atlantic hurricanes over the past 20 years, etc.

A colleague of Dr. Held, Tom Broccoli agrees with practicing patience and even suggests that “we may have to live with some ambiguity” and avoid even getting into any speculative debate.

That seems like good advice since there is always a temptation to make broad sweeping deductions from small interval data. After all, Homo Sapiens has only been seriously involved in formal agriculture for about 12,000 years! Even that is not a very long time. So, when we speak about making predictions from intervals of 20 years or so, we must be careful not to get too bold with any assumption.

As the precision and resolution of our technology continues to improve, we can expect that scientists will expand their study of just about everything to get the best possible perspective of what is actually going on in and around our planet.

With 24 by 7 world news coverage, there will always be some organization looking to make that exclusive, breaking story about something ominous about to impact our lives. It becomes our challenge to filter science “indisputable” fact from science “potential” fact from science “probably” fiction.

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