What do we know about the possible effects of climate change on tropical forests and reefs?
STRI/DICYT There’s broad agreement in the scientific community that the accumulation of carbon dioxide in the atmosphere at levels the Earth has not seen for 650 thousand years is reaching a point at which we cannot confidently predict the outcome. The presence of greenhouse gases in the atmosphere is correlated with temperature increases. 2014 was oficially the warmest year on record.
The predicted effects of climate change for Latin America not only include increased temperatures but also decreases in soil moisture, shortages of potable water and more severe drought leading to the desertification of agricultural land. Unpredictable storms producing high rainfall in some areas may also leading to flooding.
Scientists at the Smithsonian in Panama are particularly interested in how climate change may affect tropical forests and reefs. Both ecosystems support huge numbers of species and life forms vital to the rest of life in ways we have yet fully understood.
Based on pollen records and the fossils STRI paleontologists are pulling out of one of the world’s biggest coal mines in Colombia, healthy rainforests existed about 60 million years ago at even warmer temperatures than today’s. Unlike modern rainforests, they were home to a giant species of snake, the Titanoboa, that was a meter around and as long as a city bus. Giant turtles and crocodiles also lived in these swampy forests.
If there’s enough rain to keep tropical forests wet as temperature rises, the ranges of tropical plants and animals may expand into temperate areas and tropical diversity might actually increase. On the other hand, researchers in Panama discovered that tropical trees can be very sensitive to drought. If rainfall decreases, rainforest trees may die and fires may destroy larger areas of forest.
Nighttime temperatures are on the rise at the Smithsonian field station on Barro Colorado Island in central Panama. Increased nighttime temperatures result in increased seedling growth in greenhouse experiments, although it is still not clear if young, actively growing trees and mature trees will respond in the same way to changing temperatures.
One of our scientists is setting up large geodesic, glass domes where he can experimentally increase or decrease temperatures and the amount of carbon dioxide trees receive as they grow. Trees absorb carbon dioxide gas and convert it into carbohydrates. When grown in air high in carbon dioxide, they reduce the aperature of the pores in the leaves through which they take up carbon dioxide. As a result, they lose less water. This has major implications for the way water moves through ecosystems.
The Smithsonian coordinates a worldwide tree monitoring network that started here in Panama 35 years ago and now includes 60 sites in 22 countries. The network gives us the kind of information that insurance companies use to figure out what is happening to the health of human populations. Based on studies at six different sites, tropical trees are growing more slowly. Researchers disagree about whether slowing growth is a response to higher temperatures or merely a sign that forests in reserves are aging. Researchers also observe a major increase woody vines in forests from the southern US to Brazil, but are still not sure if this is related to changing environmental conditions.
At our marine stations on the Caribbean coast we’ve seen major coral bleaching events in the last several years. Corals are made of a hard skeleton inhabited by a living animal called a polyp and a plant, actually an alga, that captures nutrients for the coral. When seawater gets too warm, the algae are expelled and the corals turn white. Sometimes corals bounce back after bleaching. But often, whole coral colonies die. Smithsonian scientists want to know how resilient corals are, how quickly they adapt to changing temperatures and if there are some combinations of polyps and algae that endure warmer temperatures than others.
One of our marine biologists created a map that overlays areas where temperatures are predicted to rise on ‘dead zones’ where fish have already died from lack of oxygen because algal growth has gotten out of control. They predict that these dead zones will expand unless people take steps to radically reduce the nutrients in coastal waters—nutrients that come from sewage and agricultural runoff.
And there are many more studies about how individual animals and plants respond to changes in the environment. STRI scientists contribute to our understanding of the outcomes of all of the this long-term experiment involving all life on earth.
“I don’t have any tattoos,” said Matt Larsen, STRI Director, “but if I did, it would be a tattoo of the Keeling Curve,” referring to the iconic graph from Hawaii’s Mauna Loa observatory that precisely illustrates the precipitous increase in our planet’s atmospheric CO2 concentrations over the last few decades.