Global warming – a world of extremes and biological hotspots

An article just published in the journal Nature has helped advance our understanding of climate extremes and how the Earth of the near future will differ from our world as we have come to know it. We all know that as the climate warms, we will see more extremes – extreme heat and drought, storms and flooding – depending on where you live.

Regardless of the cause, it would be useful for policy makers and city planners to know when the future climate will depart from its normal variability. How much time do we have to act? A decade? A century?

This very question was the focus of the recent paper. The authors (Camilo Mora and colleagues at the Department of Geography, University of Hawaii) used the complete set of available climate models to calculate the year when the Earth's climate will move beyond what we have experienced in our recent past. In other words, in what year will the climate become more extreme than the year of the most extreme events we have witnessed in the last 150 years?

They looked at seven different climate variables, including temperature, precipitation, and ocean acidity. According to their results, the climate of the Earth will depart from its normal variability about 35 years from now (in approximately 2050) under business as usual human activity. On the other hand, if we take seriously the threat of climate action, we can push that date by some 20 years.

But this global average threshold is only part of the story. The authors recognized that climate change will occur more rapidly near the poles (for instance, temperature changes will be greater near the poles than in the tropics). However, the present climate in the polar regions is already more variable, and biologic systems and humans living there are more adapted to climatic shifts.

In contrast, in the tropics, given their more stable climate, it is easy for even small changes to surpass historical extreme records. In other words, the tropics will face unprecedented climates sooner. The problem is that these small climate changes pose serious challenges for people and species that are not equipped to adapt.

What this means is the authors find a "double jeopardy" situation. Humans, plants, and animals will live in the tropics and will be more susceptible to small changes, or they may reside in higher latitudes and experience the largest climatic shifts.

The study shows that the earliest expected occurrences of unprecedented climate change will occur in the tropics. That zone, with its richness in biodiversity, will see climate shifts a decade earlier than elsewhere. This is particularly true of coral reefs, which will see shifts about 20 years earlier than average. In the case of ocean pH, this variable moved into unprecedented states in 2008.

What can we do about this? It is commonly thought that increasing the natural habitats of species will be a significant help for this problem, but the authors came to a different conclusion. They point out that since the protected areas will undergo similar climatic shifts, they won't be of much use to suffering species. Also, since many of the tropical hotspot areas are located in low-income countries, the ability to fund adaptive strategies will be limited.

Finally, and perhaps most interestingly, the authors isolated key biological groups in order to compare the time they reach climatic thresholds to the average globe. Some of the biggest losers – coral reefs (already mentioned), mangroves, seagrasses, marine reptiles, cephalopods, and marine fish – will experience far earlier climate disruption than the rest of us. That should give no consolation; in a world as interconnected as ours, we will all feel these climate shifts sooner rather than later.

As for people, some 5 billion people, mostly in developing countries, could be facing unprecedented climates by 2050.

In my second paragraph, I presented a bit of a red herring by asking us how long we have to act. The real answer is, we are out of time. As this study shows, and other studies reinforce, many of the climate changes are already baked into the system. Even if we take significant and meaningful actions, many of the deleterious impacts will occur anyway.

So, should we do anything if we are already committed to some climate change? Failing to act will simply test our capabilities to adapt earlier and, unfortunately, we may not be ready for it (overwhelmingly unprecedented climates will occur among developing countries). Alternatively, we could act now, which will buy us and species critical time for adaptation. Failing to act risks saying goodbye to our climate and facing the implications that come with its departure.

While we ponder this, readers can go to Dr. Mora's site, which includes interactive maps of future climate change impacts.

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Posted by John Abraham on Wednesday, 9 October, 2013

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