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Scientific Knowledge is Priceless

Ecological Consequences of Climate Change

Terry L. Root

For migratory birds like the Rufous Hummingbird, will the timing of food availability change? Tom Grey photo.
This Observer features PRBO's work related to climate change. First, a survey of some effects in nature, for which we thank ecologist and climate-change expert Dr. Terry Root. A researcher and professor, she has served on the Intergovernmental Panel for Climate Change (co-recipient of the 2007 Nobel Peace Prize) and is also member of PRBO's Board of Directors and Science Advisory Committee.—Editors

Over the last 100 years, the Earth's average surface temperature has risen by about 1.1F (0.8C). This may not sound too alarming: after all, the temperature difference in California between winter and summer months is greater than that. But to put this in perspective, consider the transition that began about 20,000 years ago: ice sheets covering much of the northern United States and elsewhere began to melt; sea level rose 100 meters; plants and animals in the Northern Hemisphere moved northward; and many species went extinct. The rate of warming across the globe then was about 0.9–1.8F (0.5–1C) per thousand years.

Yes, the warming over the last 100 years is equivalent to prehistoric warming that took 1,000 years. Based on our current rate of greenhouse gas emissions, climate scientists project that the global average temperature could increase by 11F (6C) and even more over the next hundred years. What will such rapid change mean for ecological systems?

With the change in temperature recorded over the past century, we already see species changing on every continent and in the oceans.

Changes in distribution. As the globe warms, some species are extending their ranges poleward and upward in elevation, into areas that were previously too cool for them to colonize. The species originally at the tops of mountains or at the continents' colder edges have nowhere to move; they are having to interact with new species while also coping with warmer temperatures.

To understand how serious these effects on natural systems may be, scientists are looking into the future with tools such as predictive and distributional modeling.
Common Murres breeding on the Farallon Islands depend upon seasonal upwelling and food productivity in the ocean. Ron Levalley photo.

Changes in timing. Species on every continent are already shifting the timing of seasonal events: frogs are breeding earlier, cherry trees are blossoming earlier, and leaves are turning color later in the autumn. Information on 115 species of plants and animals from around the globe shows the timing of a spring event advancing by about five days per decade, on average, over the last 30 years. Quantifying such shifts in seasonal timing requires data from at least 20 years of long-term monitoring—one of the many strengths of PRBO's research.

One consequence of seasonal events shifting in time could be that a species' food source is not available when needed. On the Farallon Islands, for example, Common Murres are among the colonial seabirds that rely on the timing of ocean upwelling for food to fuel their breeding cycle.

Changes in the oceans. Increased concentrations of greenhouse gases will affect marine ecosystems, as well. Changes in sea level associated with global warming may inundate important nesting areas for marine birds and shorebirds. Changes in ocean currents may influence the distribution and seasonal availability of food.

Scientists now are realizing that increases in atmospheric carbon dioxide (CO2) can also cause profound changes in ocean chemistry. When CO2 from the atmosphere is taken up by the oceans, the water becomes more acidic, preventing clams, snails, and other invertebrates from forming calcium-based shells and skeletons. This is beginning to happen, and scientists project that by the year 2100 ocean acidity will be greater than at any time during the last 20 million years.

Extinction. Rapid global warming is already causing some species to face the ultimate, irreversible change—extinction. The threat of extinction posed by climate change today may be greater than what species faced in the past, for two reasons. First, human-induced climate change is occurring about ten times faster than prehistoric changes in climate—perhaps too rapidly to accommodate evolutionary processes that might enable species to adapt. Second, species today must also cope with other human-caused stresses, such as land-use change and invasive species.

Many biologists, me included, believe we are standing at the brink of a mass extinction that would be caused by one species—us. If global mean temperatures rise 2.3–4.1F (1.3–2.3C) above today's mean, then roughly 20–30% of the 1.7 million identified species could be facing a high risk of extinction. Some 400,000 species could vanish.

Facing the crisis

History shows that when response to a crisis requires more resources than are available, having a plan in place before the crisis is well under way results in much less harm. As we consider ways to protect biodiversity from rapid climate change, prioritization will likely be necessary. We will not have the needed resources, such as biological knowledge, people power, and political will, to save all 400,000 species. Ranking species to try and save with the resources available should help to minimize the number of extinctions. This is not how we would like to proceed, of course, but the limits to our knowledge and resources will necessitate concentrating on species we have the best chance of saving.

In terms of a lasting solution, what can we do? Lots! Just as each of our votes counts, and our taxes contribute to our governance, the actions we all take add up. Organizations, too, can focus their efforts— for example, with new strategic initiatives like PRBO's. Conservation scientists must do as PRBO is doing—monitor species so that we know when there is trouble; gain basic understanding to help us tailor survival plans; model what might occur in the future; and understand the capacity of species to move to and exist in new habitats. The practical value of knowledge like this is priceless.