This 2009 file photo shows Ice Fjord of Ilulissat in Greenland. The Greenland ice sheet has lost 1,500 billion tonnes of ice since 2000. AFP/AFP/Getty Images

You don't need a Ph.D. in biology to tell the climate is changing in Minnesota and the world. Ask a gardener about the changes in Twin Cities plants or a fisherman pulling an ice house off the lake weeks earlier than when he was a kid.



The atmosphere is warmer. But is that a problem? Is global warming simply a temporary, cyclical phenomenon or evidence of a slow motion crisis? How much of what's happening can be traced to humans and their industries? What, if anything, should be done to stop climate change?

IS CLIMATE CHANGE REAL?

The scientific evidence of global warming is hard to ignore. The National Oceanic and Atmospheric Association's "Ten Signs of a Warming World" cites data showing rising air temperatures over land and sea, shrinking glaciers and rising humidity.

The federal Environmental Protection Agency notes the evidence is overwhelming that average temperatures here and across the globe are rising.

The Earth's average temperature has increased since the late 1800s, when people started burning a lot of coal, oil, and natural gas. Worldwide, 2000-2009 was the warmest decade ever recorded. In the United States, seven of the top 10 warmest years on record have occurred since 1990.

In Minnesota, the state's climatologists have mapped it out. Orange, green and blue mark where the temperatures have risen.





The state climatology group writes, "Minimum or 'overnight low' temperatures have been rising faster than the maximum temperature. Winter temperatures have been rising about twice as fast as annual average temperatures."

And 2012 is likely the warmest year on record in the Twin Cities and most of Minnesota, say Greg Spoden with the Minnesota Climate Working Group.

Need more data? MPR meteorologist Paul Huttner notes:

• 2012 marks the 36th consecutive year, since 1976, that the yearly global temperature was above average. Anyone under age 36 has never lived through a year cooler than the 20th Century global average.



• The 10 warmest years globally since 1880 have all occurred since 1997.







Among the public, "Nearly 4 out of 5 Americans now think temperatures are rising and that global warming will be a serious problem for the United States if nothing is done about it, a recent Associated Press-GfK poll finds. "Concerns are growing fastest among people who don't often trust scientists on the environment."

The U.S. Global Change Research Program, a working group of 13 federal departments and agencies, says, "Global warming is unequivocal and ... is due primarily to human-induced emissions of heat-trapping gases.... Climate changes are underway in the United States and are projected to grow."

WHEN DID CLIMATE CHANGE BECOME SUCH A BIG DEAL?



Global warming became a hot political issue in 1997 with the negotiation of the Kyoto Protocol, an international treaty that called on the developed, industrialized nations to slash their emissions of so-called greenhouse gases that contribute to global warming.

Greenhouse gases trap heat in the atmosphere, slowly raising the temperature of the planet, leading to climate change. Those gases come largely from industry, agriculture and automobiles. Carbon emissions -- the stuff that comes out of cars and other internal combustion engines, represents 60 percent of the "enhanced greenhouse effect" that's tied to climate change.

Slashing emissions meant nations, particularly the United States, would have to pull back on the use of coal, oil and gasoline -- the lifeblood of the American economy. Since then, U.S. leaders have offered plans to reduce emissions but have refused to sign the Kyoto Protocol given the concerns about the damage it might do to the U.S. economy and jobs, as well as the fact that newly industrializing nations wouldn't have to abide by the treaty.

While the politics are tricky, the research since Kyoto continues to confirm the globe is warming because of greenhouse gas emissions. The National Academy of Sciences wrote in 2001:

Greenhouse gases are accumulating in Earth's atmosphere as a result of human activities, causing surface air temperatures and subsurface ocean temperatures to rise. Temperatures are, in fact, rising. The changes observed over the last several decades are likely mostly due to human activities, but we cannot rule out that some significant part of these changes is also a reflection of natural variability.

Former Vice President Al Gore put the global warming issue permanently in the spotlight with his 2006 movie, "An Inconvenient Truth." Gore called global warming a "planetary emergency" and argued it wasn't simply a political issue but a moral challenge to civilization.

The movie emphasized what individuals could do to reduce their carbon footprint. The more troublesome question: What should governments be doing to force lower emissions by individuals and industries?

WHAT DO ADVOCATES WANT GOVERNMENT TO DO?



Gore and others sounding the alarm on climate change have pressed for government policy to cut carbon emissions. That include subsidizing research and development of renewable, "green" energy technology along with taxes on gasoline, coal and other carbon-based products.

Some advocates have pressed for the U.S. and other governments to create a "cap and trade" system that would set a ceiling on emissions and then lower the ceiling, slowly, while giving businesses the option to pay to produce more emissions.

"Cap and trade is the most environmentally and economically sensible approach to controlling greenhouse gas emissions, the primary driver of global warming," the Environmental Defense Fund argues.

The "cap" sets a limit on emissions, which is lowered over time to reduce the amount of pollutants released into the atmosphere. The "trade" creates a market for carbon allowances, helping companies innovate in order to meet, or come in under, their allocated limit. The less they emit, the less they pay, so it is in their economic incentive to pollute less.

Others advocate carbon taxes placed directly on coal mines, oil wells, oil tankers and other points of origin for carbon emissions.

Tax policy can be hard to pass, however. In December 2012, the Natural Resources Defense Council pressed for a faster route to government policy. The group argued that states, together with the Environmental Protection Agency, have the power now under the Clean Air Act to set new carbon pollution standards that will cut existing power plant emissions 26 percent by 2020.

"We know where the pollution is," the group writes. "Now we just have to go get it."

WHAT ARE THE ARGUMENTS AGAINST GOVERNMENT ACTION?



Critics of government intervention see the issue very differently, questioning the competency of government agencies and arguing that politics, more than science, is guiding the decision making.

The Heartland Institute, a Chicago-based nonprofit group skeptical of global warming research and opposed to government intervention to stop it, has blasted United Nations officials for "bias and incompetence" on the climate change debate. It's highlighted reports refuting the UN arguments that global warming is hurting plant growth, slammed government subsidies for wind power.

It's also helped lead the charge to stop Congress from enacting carbon taxes. "The environmental movement needs voices devoted to sound science and market-based, rather than government-based, solutions to environmental problems," the group writes.

Other skeptics question if politically motivated scientists are messing with the data in order to get governments to implement restrictions they think are best on carbon emissions. One skeptic, Anthony Watts, calls it "noble cause corruption." He told PBS NewsHour:

I was a victim of that at one time, where you're so fervent you're in your belief that you have to do something. You're saving the planet, you're making a difference, you're making things better that you're so focused on this goal of fixing it or changing it that you kind of forget to look along the path to make sure that you haven't missed some things.

Some critics also note the despite the financial and political capital spent on the Kyoto Protocol, the treaty so far has failed to slow carbon emissions worldwide, arguing that, however you see climate change and its origins, international policy making has failed.

WHERE IS THE DEBATE HEADED?



If you've zoned out on the global warming, climate change debate the past few years, you're forgiven. There's been little change in the nature of the discussion -- an endless loop about political motivations and trash talk over which scientists, groups and data can be trusted.





There are signs, though, that entrenched debate may be shifting.

Marathon negotiating sessions at a recent international climate change conference produced an understanding, at least, that China, India and other developing industrialized nations need to be part the next deal to cut carbon emissions.

In December, Great Britain's Guardian newspaper wrote, "Countries are working towards a new global agreement on climate change that would, unlike the Kyoto protocol, require cuts in greenhouse gas emissions from both developed and developing countries, to be signed in 2015 and come into force from 2020."

That's a key change. One key British economist estimates those emerging industrial economies "now make up the bulk of the world's carbon emissions," the Guardian reports.

And while leaders in Asia's rapidly developing industrial nations love the wealth produced by the economic activity, they can no longer ignore that carbon-based pollution is killing large numbers of their citizens.

Slowly, the nature of the debate seems to be shifting away from economy-vs-planet toward national security. The U.S. National Security Council's "Global Trends 2030" report, published in December, tied climate change to global security. Among the report's warnings:

Demand for food, water, and energy will grow by approximately 35, 40, and 50 percent respectively owing to an increase in the global population and the consumption patterns of an expanding middle class. Climate change will worsen the outlook for the availability of these critical resources.

Contacts in Africa worry about climate change creating new social and economic tensions that could flare into civil conflict.

Impacts from climate change, including water stress, in addition to low economic growth, rising food prices, and energy shortages will pose stiff challenges to governance in Pakistan and Afghanistan.

Worrisome stuff. Regardless of your politics or how you view the scientific data, there's no doubt the national security question has the potential to alter the landscape of the climate change debate.



(NOTE: The Guardian newspaper's "Carbon Emissions" page is a great resource for international news and insight on climate change / global warming. Locally, the Minnesota Climatology Working Group maintains a comprehensive page on climate change in Minnesota.)



(MPR's chief meteorologist Paul Huttner and University of Minnesota climatologist Mark Seeley contributed to this report)