"There's a very limited pool of people going into graduate school to specialize in climatology," says climatologist Brent Yarnal. He's a professor at Pennsylvania State University.

"We have more research assistantships and post-doctoral research fellowships than we have applicants to fill them, especially from here in North America."

Some people think climatologists do the same thing as meteorologists. But there's a difference. Meteorologists make short-term predictions. Climatologists forecast long-term trends. They study factors like air currents, the oceans and temperatures that cause shifts in climate.

These changes can have big effects on humans, animals and plant life. Things like food production, irrigation, life expectancy and the survival of endangered species are all affected by the climate.

Many climatologists are modelers. They have strong backgrounds in physics and math and use computer programs to simulate the Earth's climate. They study the past and present to predict future trends.

Many other disciplines can overlap with climatology because the climate has such large implications for life on the planet.

Many scientists do climate research but don't call themselves climatologists. Social scientists look at how the climate affects societies and how policies impact climate change.

Climate scientists might also have a background in life sciences such as botany, zoology or entomology. They might study oceanography, meteorology, computer science and many other fields.

It's complex and demanding work. But it's an exciting and rewarding field for those who make a career of it.

Holly Dolan is a social science researcher with a PhD in geography. She looks at climate change in terms of adaptation and vulnerability. She's interested in how society's policies are influenced in regard to climate change.

She says climate researchers get a lot of satisfaction from their work.

"I think it's incredibly interesting and has some fundamental implications for human societies," she says. "It has huge implications for societies, for sustainable development, for human-environment interaction."

Most people who earn a PhD in climatology have backgrounds in physics and mathematics. Some have also studied chemistry, computer science and geography.

Andrew Weaver is head of a climate-modeling group at a university. He says a lot of his students want to study math and physics relevant to society, so they find climatology very appealing.

Also, there are plenty of jobs.

"Every student I've ever had has gotten a position," says Weaver. "Not only that, they can be selective as to where they want to go."

Fred Herfst agrees about the large demand. He's executive director of the Canadian Institute for Climate Studies. He says many climatologists at the master's and PhD levels are retiring.

"There's more opportunity now, and the universities over the last five to 10 years have not produced enough, so there's definitely a period right now where there's a scarcity of people," Herfst says.

Climatologists work for government at the federal and state level. They also work as professors and researchers at universities.

There are also opportunities with nonprofit organizations and private companies. Even oil companies, utilities and steel companies hire climate scientists to help develop policy.

"Right now, a lot of hiring is going on at the PhD level, not so much at either the master's or the undergrad level," says climatologist Bob Whitewood.

Whitewood says the complexity of the work is increasing the level of education required. "Often, there's a lot of independent thought required in the research, so there's that training that you get with a PhD that you wouldn't get with just an undergrad degree."

There are literally thousands of climatologists in North America, says Yarnal. Only a few have PhDs in climatology, however.

Most have a degree in something else, such as meteorology or geography or hydrology. But they have chosen to specialize in climate science. Because of this, it's impossible to estimate the total number of climatologists, says Weaver.

Climatologists can make very good money. "Starting salaries are usually around $40,000 a year, but if they stay and become part of the local establishment, these people as senior researchers can earn $60,000, $70,000, and much more," says Yarnal.

Weaver agrees with the "much more" part of Yarnal's estimate. "Senior researchers can earn a heck of a lot more," Weaver says. "I have a student earning $120,000 as a junior faculty member in New York."

Weaver stresses that climatology is a demanding field. You'll earn that paycheck. "You've got to be good at what you do," he says. "If you excel at physics and math, and then you decide to take that into climate science, you'll do really well.

"Climate is going to be a major challenge for society as a whole over the next century -- a huge challenge," Weaver adds. "To be positioned in this area is kind of strategic."