The coast of Belize is a magical place, and, like the rest of the Caribbean, it experiences its share of problems with tourism and overfishing, but it’s long been a diver’s dream. Diving on a healthy coral reef can truly take your breath away. Fish of every description dart among pillars of corals and waving seafans, and every crevice is filled with life. Seeing a healthy reef is like suddenly being able to experience color after living a lifetime of black and white.
I was fortunate to begin working in Belize as a graduate student at the University of Washington, and in 1991, I made my first trip to the field station managed by the Smithsonian Institution on Carrie Bow Cay. I managed to make a trip almost every year after that, studying the effects of water movement on feeding by corals.
In 1998, something terrible happened.
I returned to one of my favorite sites, in an area known as the Pelican Cays, to find every last bit of coral was dead, and the entire reef, now consisting of ghost skeletons, was a massive farm for oozing algae. Colleagues who had documented the event warned me, but even so I was not prepared for the devastation that I observed. A subtle increase in water temperature caused the corals to “bleach,” a phenomenon in which corals lose the symbiotic microorganisms, known as zooxanthellae, living in their tissues. The life and death of these tiny creatures in turn had a cascading impact on the entire reef ecosystem.
The events of 1998 didn’t raise alarm bells with the general public, but it did stun many of us working in field biology. The death we scientists observed; a change as little as 1 degree Celsius above normal, can cause severe damage to corals and other organisms. In the last decade, coral bleaching events, and other mortality related to climate change, has been documented worldwide.
Climate Change a Fact, Not a Faith
Like many scientists, I didn’t start out studying climate change; it more or less became a fact of life when the organisms I was studying started to die.
Since that day at Pelican Cays, I have been fortunate to travel to many sites around the globe, ranging from the waters of the southern Pacific Ocean to the crashing surf along the Pacific coast of North America, and what I see matches the observations made by what now is an army of scientists: The Earth’s flora and fauna are changing — shifting their geographic locations, altering when they reproduce or dying wholesale — as a result of human-induced global warming.
The question before the scientific community is no longer, “Is climate change due to human activities happening?” Of that we are certain.
Instead, the question is, “Where, when and with what magnitude are effects most (and least) likely to occur?” Most importantly, how can we use science to prepare for, and perhaps minimize, the damage that is on the horizon? While this concept of “adaptation to climate change” in no way negates the challenges before us in terms of mitigating greenhouse gas emissions, it does suggest that there are positive, forward-thinking steps that we can take to prepare for a warmer world.
For many Americans, the idea of global climate change seems like a far-away concept, an idea dreamt up by scientists in their laboratories. That some still talk about “belief” — a matter of faith more so than facts — in findings that have long been accepted by the scientific community speaks volumes about the general public’s understanding and acceptance of global climate change.
While considerable uncertainty exists in predicting just how much climate will change in the future, scientists agree that we are committed to at least some change, likely a minimum of 2 degrees Celsius and perhaps much more, over the next 50 to 100 years. In other words, even if we stopped all carbon emissions now, the Earth has sufficient inertia in its climate system that changes will continue to occur, and no one is holding their breath that emissions will be shut off overnight.
Change is much more drastic at some sites than others, and there remain places of refuge. But, the message is clear: Climate change is already altering the world’s ecosystems, and is therefore a threat to us humans. While it may appear as simply a matter of writing off these impacts as the concerns of environmental left-wingers, even a cursory look shows that climate change affects everyone — and in ways that many of us don’t realize. Global warming strikes at the heart of our food supply, it magnifies the rate at which we contract disease and curtails our ability to obtain fresh water.
While climate change will create winners and losers, the overall prognosis is not encouraging. There is good news, however. We now have methods for predicting where some of these changes are most likely, and in doing so, we may be able to better prepare for a warmer world.
The relatively new science of ecological forecasting could be a key to preparing for a world turned upside down by global warming. Rather than simply documenting a list of dead and dying species, we can identify “trouble spots” that demand our attention and, in turn, know how and when it is best to act.
Importantly, global warming is often the “trigger that fires the bullet,” and changes in temperature often interact with other stressors, such as pollution. Sources of stress that affect the health of the environment are in many ways directly analogous to those that impact human health; when a person has poor nutrition, their body is less able to fend off disease and to recover from injury.
Even in cases where temperature increases do not cause wholesale mortality, they often push organisms to the point where they can no longer tolerate other environmental insults. In this same way, we can minimize the effects of global warming by decreasing other factors such as nutrient runoff, overfishing and heavy metal toxicity — but only if we know how to identify the most critical patients. Thus, while forecasting and other forms of “adaptation to climate change” do not rid us of the need to mitigate the underlying problem of greenhouse gas emissions run amok, the method does provide a means of focusing time, energy and money.
Knowing how to “triage” the natural world first requires that we understand how nonhuman organisms see the world. As it turns out, this may be more difficult than we think.
Small Change, Big Trouble
We are wired differently than most other species on Earth in how we experience heat and temperature.
Unlike virtually all other plants and animals, our metabolism (and that of birds and mammals) gives us tight control over the temperature of our bodies. We, therefore, don’t “sense” changes in the world nearly as much as most other organisms.
For humans, air temperature is one of the most familiar indicators of how “hot” or “cold” the weather is, as the difference between air temperature and the temperature of our bodies determines how rapidly we lose (or gain) heat. When the wind blows, increasing heat loss, we add a wind chill factor to determine an “effective air temperature.”
Here in the South, as I quickly learned upon arrival in South Carolina, we calculate a “heat index” to reflect that high relative humidity reduces the ability to shed heat through perspiration. Except for extreme circumstances of heat stroke and heat exhaustion (which are indeed a worry under climate change in many parts of the globe), our body temperatures remain relatively constant at a core temperature of 37 degrees Celsius.
When our bodies start to warm above normal, we slow down cellular metabolism and open up our pores, increasing cooling through evaporation and convection. When we become too cold, our bodies kick up metabolism or, in the extreme, shiver to produce heat.
The average temperature of the Earth’s surface has increased by 1.2 degrees Fahrenheit (0.7 C) over the last century (and much more in places like the Arctic). Does this matter to us as organisms? After all, if we feel a slight temperature increase, we are likely to simply brush it off by cranking up the air conditioning or delighting that spring has come that much earlier.
Slight increases in temperature affect mammals such as humans by forcing us to stay in cool places more frequently. For many people, this is usually not an issue, although recent projections suggest that even moderate physical activity during the summer may push people living in urban “heat islands” close to heat stroke. This was vividly illustrated in France in 2003, when thousands without access to air conditioning died during a heat wave.
Herein lies one of the largest direct effects of climate change on human physiology. While small changes in average temperature may be relatively easy to contend with, climate change is causing a marked increase in the frequency of extreme events — and these can be deadly.
For most other plants and animals, lacking our metabolism and our air conditioning, a shift in environmental temperature means a change in body temperature. For organisms living close to their thermal limits, this can mean big trouble.
Like humans, these organisms gain and lose heat from their surrounding environment. Unlike us, they generally have a very low level of metabolism, and so their bodies get warmer or colder as the surrounding weather heats or cools.
Think about walking barefoot across a parking lot on a sunny summer day. In the same way that short-wave radiation from the sun is converted into heat energy on the asphalt surface, so is it converted to heat in the bodies of animals, including us.
Animals of course have some behavioral control over the amount of sun that hits their bodies and (except for teenagers trying to tan) humans are among the best examples. Such control is important because even a few degrees above normal body temperatures can be deadly. For birds and mammals, trying to stay cool can come at a significant cost; time spent lying in the shade means time not spent hunting for food.
Some of the most severe impacts, however, are not likely to be felt through impacts on human body temperature but through indirect effects on animals and plants around us that serve as our food as well as our nemeses.
We know from decades of studies that the temperature of a plant’s or animal’s body is one of the most important factors affecting its growth, reproduction and survival. Virtually every physiological process is affected by body temperature, and as we have seen, many organisms live very close to their limits of temperature tolerance.
As a result, even small changes in weather and climate can push these animals and plants over the edge as they hit highs during the day or lows at night. Critically, these effects are not uniform across the globe, and there are winners and losers. An animal or crop that may fail miserably due to climate change at home may do well at a new location. Conversely, pests and diseases that are now held in check by weather may suddenly be able to spread.
We Can Do Triage
We have tools that may help us to predict where and when climate change is most likely (or least likely) to affect plants and animals. Scientists have long understood that weather and climate drive the physiology and ecology of organisms. Now, armed with new remote sensing platforms, high power computing to generate models and microchips to measure temperature in even the most extreme parts of the planet, we are gaining new insights into how climate is driving the world’s flora and fauna.
Like everything else, animals obey the laws of physics. They lose heat via convection to the surrounding air (just as we do on a windy day), and they gain heat from the sun. Importantly, each organism has a different interaction with its environment. So, for example, a dark-colored organism will absorb more heat than will a light-colored creature. Depending on the color of their wings, for example, two species of butterflies sitting side-by-side can experience body temperatures that are 2 C to 3 C different from one another.
Likewise, organisms that are more “streamlined” will lose heat more slowly to surrounding air (when they are hotter than the air) or will gain heat more slowly when the surrounding air is hotter than their bodies. Look at the ears of many mammals, such as elephants, which are used to shed heat when it gets warm. In contrast, animals living in colder climes tend to have compact bodies with smaller appendages.
As a result of these varying and interacting mechanisms of heat exchange, two organisms exposed to precisely the same environmental conditions can have very different body temperatures and will suffer or thrive accordingly. Moreover, the organism’s temperature is often much higher than the temperature of the surrounding air.
The end result is that, if we could view the world in terms of temperature (as we can do using a camera that, like a pit viper, is sensitive only to infrared), we see that the natural world is much more variable in terms of the temperatures of organisms than we often assume.
Not only do plants and animals determine their own temperatures through different colors, shapes and surface wetness, but the amount of sun hitting any portion of the ground can have huge effects on temperature; studies have shown that the difference in the temperature of animals living on a shaded surface can be 15 C colder than that of an animal sitting in the sun only a centimeter away.
Using simple physics, we can calculate all of the sources and losses of heat, and we can estimate the temperatures of a range of plants and animals. The results often show patterns of body temperature hidden to the human eye, and so help us to predict where and when climate change is most likely to alter ecosystem function.
Ecological forecasting explores how organisms interact with their world to predict the temperatures of animals and plants or the cost to them of maintaining a constant temperature. Results also show that we can use these models to reliably predict past (and therefore future) changes in patterns of mortality in the field.
For example, David Wethey and Sally Woodin recently studied the role of winter water temperatures in determining geographic distributions of barnacles in Europe, and their discoveries strongly suggest we can reliably predict past shifts due to climate change, and that we can thus use these methods to predict future shifts.
Specifically, they took data from more than 100 years of scientific papers, they compared existing range boundaries with those in the historical record and found that the southern geographic limit retreated by 300 kilometers (or 186 miles) at a rate of 15-50 kilometers every decade. Previous studies show that this species cannot reproduce when winter temperatures exceed 10 C. They compared long-term records of winter temperature against range shifts. The results were a near perfect match.
Work in my lab has shown that the likely locations of damage due to climate change can often occur in unexpected locations. Using a series of microcomputers that match the thermal characteristics of intertidal bivalves, we have measured patterns in body temperature along the west coast of North America since 1998; in some cases, we now have records from every 10 minutes.
These “robomussels” show an unusual pattern. Instead of a steady increase in mussel temperature moving from north to south, populations experience a thermal “mosaic” of alternating “hot” and “cold” spots, and in several cases, populations in Washington and Oregon are as hot or hotter than those in California. While several factors contribute to this pattern, the largest influence is the timing of low tide. In the north, low tides tend to occur mid-day in summer, when conditions are hottest. At many southern sites, animals are underwater during these hot portions of the day.
We have also developed computer models that predict body temperatures to within several degrees using data from weather stations and satellites, and current efforts under way in David Wethey’s lab will eventually allow us to predict patterns of temperature on a global basis.
Nicola Mitchell and co-workers have used physics-based models to predict patterns of survival and reproduction of Tuatara, a rare and ancient lineage of lizards that have what is called “temperature-dependent sex determination.”
As is the case for organisms such as turtles, the sex of a baby Tuatara is determined by the temperature of its nest. Mitchell’s models suggest that in the near future, all of the hatchlings from nests along the coast of New Zealand will be male — and thus, without intervention, these populations are likely to go extinct. However, by knowing where trouble spots are likely to emerge, it may be possible to either shade nests or move eggs to other sites along the coast, saving this species.
Because we know that there will be winners and losers from climate change, in the same way as the Tuatara example, we may be able to use information about stress in organisms such as crops and shellfish to prepare for a warmer world — in short, siding with the winners and cutting losses from the losers.
Thus, while some crops are predicted to decrease in productivity as a result of increased temperatures and changes in precipitation, others are expected to do well under higher levels of carbon dioxide. By predicting where these shifts are likely to occur, we can help farmers pick the best agricultural strategies. Similarly, we can locate regions for protecting biodiversity that are not only suitable as biological hotspots now but will continue to serve as refugia in the future.
Make no mistake, climate change is real, and reducing greenhouse gas emissions remains the top environmental priority of our time. But we are not helpless in preparing for these changes. Scientists, policymakers and members of the business community must create a new paradigm for how we work collaboratively. Only through these partnerships can we creatively and productively plan for a future that we can all live with.
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