WASHINGTON (Reuters) - Climate change will make wildfires in the U.S. West, like those now raging in parts of Colorado and New Mexico, more frequent over the next 30 years, researchers reported on Tuesday.

More broadly, almost all of North America and most of Europe will see an increase in wildfires by the year 2100, the scientists wrote in the journal Ecosphere, a publication of the Ecological Society of America.

The U.S. Southwest - Arizona, New Mexico and Texas - is the fastest-warming region of the United States, and this warming trend will worsen droughts, alter growing seasons and increase wildfire risk, the non-profit research organization Climate Central reported.

On Tuesday, 20 large wildfires were burning in eight Western states, from Idaho and Wyoming to California and Arizona, according to the U.S. Forest Service. A map of active fires is online at activefiremaps.fs.fed.us/ .

Using satellite-based fire records and 16 different climate-change models, an international team of researchers found that while wildfires will increase in many temperate zones due to rising temperatures, fire risk may actually decrease around the equator, especially in tropical rainforests, because of increased rainfall.

"In the long run, we found what most fear - increasing fire activity across large areas of the planet," said lead author Max Moritz of the University of California-Berkeley.

"But the speed and extent to which some of these changes may happen is surprising. These abrupt changes in fire patterns not only affects people's livelihoods, but also they add stress to native plants and animals that are already struggling to adapt to habitat loss," Moritz said in a statement.

Co-author Katharine Hayhoe of Texas Tech University said this study gives a unique global perspective on recent fire patterns and their relationship to climate.

Climate scientists, including those affiliated with the United Nations Intergovernmental Panel on Climate Change, have projected that more frequent wildfires would be likely in a warming world. Other effects of global warming include more severe storms, floods and droughts, these scientists have said.

CONTROLLED FIRES

In a separate study, researchers approved of the intentional setting of controlled fires, a wildfire-fighting technique that has sometimes raised questions about its impact on wildlife.

Writing in the June issue of the journal BioScience, researchers at the University of California-Berkeley reviewed two decades of research on the ecological impact of cutting forest wildfire risk, especially in the southern Sierra Mountains, where precipitation was at half of normal levels.

The idea behind so-called controlled burns is to reduce the amount of fuel that would feed a wildfire. The new study found that these fuel-reducing fires do not cause substantial harm.

"The few effects we did see were usually transient," Berkeley's Scott Stephens said in a statement. "Based upon what we've found, forest managers can increase the scale and pace of necessary fuels treatments without worrying about unintended ecological consequences."

A warming climate makes the carbon dioxide stored in forest soils decompose faster, sending more climate-warming carbon into the atmosphere, researchers at the University of California-Irvine and elsewhere reported Monday in the journal Proceedings of the National Academy of Sciences.