Walk through the Amazon rainforest today and you will find it steamy, warm, damp and thick. But if you had been there around 15,000 years ago, during the last ice age, would it have been the same? For more than 30 years, scientists have been arguing about how rainforests might have reacted to the cold, dry climate of the ice ages, but till now, no one has reached a satisfying answer.

Rainforests like the Amazon rainforest are important for mopping up CO₂ from the atmosphere and helping to solve global warming. Currently the trees in the Amazon rainforest take in around 500 million tons of CO₂ each year, equal to the total amount of CO₂ given off in the UK each year. But how will the Amazon rainforest react to the future climate change? If it gets drier, will it survive and continue to draw down CO₂? Scientists hope that they will be able to learn in advance how the rainforest will manage in the future by understanding how rainforests reacted to climate change in the past.

Unfortunately, collecting information is incredibly difficult. To study the past climate, scientists need to look at fossilized pollen(花粉) kept in lake mud. Going back to the last ice age means drilling down into lake sediment(沉积物), which requires specialized equipment and heavy machinery. There are very few roads and paths, or places to land helicopters and aeroplanes. Rivers tend to be the easiest way to enter the rainforest, but this still leaves vast areas between the rivers completely unsampled(未取样). So far, only a handful of cores have been drilled that go back to the last ice age and none of them provide enough information to prove how the Amazon rainforest reacted to climate change.

A dragonfly barely an inch and a half long appears to be the animal world's most productive long-distance traveler—flying thousands of miles over oceans as it migrates from continent to continent—according to newly published research.

Biologists who led the study say the evidence is in the genes. They found that populations of this dragonfly, called Pantala flavescens, in Texas, eastern Canada, Japan, Korea, India, and South America, have such similar genes that there is only one likely explanation. Apparently—somehow—these insects are traveling distances that are extraordinarily long for their small size, breeding (繁殖) with each other, and creating the common worldwide gene pool.

But how do insects from different continents manage to meet and hook up? Ware says it appears to be the way their bodies have evolved. "These dragonflies have adaptations such as increased surface areas on their wings that enable them to use the wind to carry them. "

Dragonflies, in fact, have already been observed crossing the Indian Ocean from Asia to Africa. "They are following the weather," says Daniel Troast, who analyzed the DNA samples in Ware's lab. "They're going from India where it's the dry season to Africa where it's the wet season, and apparently they do it once a year. "

Wetness is a must for Pantala flavescens to reproduce, and that, says Ware, is why these insects would be driven to even attempt such a dangerous trip, which she calls "a kind of suicide". The species depends on it. While many will die on the route, as long as enough of them make it, the species survives.

For the moment, the details of this extraordinary insect travel are a best educated guess. Much more work is needed to bring many loose ends together. Ware and Troast hope that scientists can work on plotting those routes.

In the past 50 years, the amount of water in the open ocean with zero oxygen has gone up more than fourfold. In coastal waters, including river mouths and seas, low-oxygen sites have increased more than tenfold since 1950. Scientists expect oxygen to continue decreasing even outside these zones as Earth warms.

"Oxygen is fundamental to life in the oceans," said Denise Breitburg, a marine ecologist from the Smithsonian Environmental Research Center. "The decline in ocean oxygen ranks among the most serious effects of human activities on the Earth's environment. Actually, it's a mass loss to all the support services that rely on recreation and tourism, including hotels and restaurants and taxi drivers and everything else. The reverberations(影响) of unhealthy ecosystems in the ocean can be extensive. "

In areas traditionally called "dead zones", like those in the Chesapeake Bay and the Gulf of Mexico, oxygen plummets(速降) to such low levels that many animals die. As fish avoid these zones, their habitats become smaller and they're easier to be attacked or caught. But the problem goes far beyond "dead zones". Even the smaller oxygen decline can prevent growth in animals, hinder reproduction and lead to disease or even death. It can also cause the release of dangerous chemicals such as nitrous oxide, a greenhouse gas up to 300 times more powerful than carbon dioxide. While some animals can boom in "dead zones", overall biodiversity falls.

Climate change is the key criminal in the open ocean. Warming surface waters make it harder for oxygen to reach the inside of the ocean. Furthermore, as the ocean as a whole gets warmer, it holds less oxygen. In coastal waters, too much nutrient pollution from land creates algal blooms, which use up oxygen as they die and break down.

People's livelihoods are also on the line, the scientists reported, especially in developing nations. Smaller fisheries(渔场) may be unable to relocate when low oxygen destroys their harvests or forces fish to move elsewhere. So we humans have to carry on a war now and win the war.