Climate change remains controversial, with a significant number of Americans saying it's exaggerated and many lawmakers disputing the science.
At the same time, climate scientists are nearly unanimous and have found new evidence that it has already begun, with the past decade the warmest ever recorded for global temperatures.
That's having effects that can be seen from the Arctic Circle to Africa, including melting permafrost, more pollen and fewer butterflies.
Below, five notable ways climate change can already be seen.
What's happening: Permafrost, the layer of frozen topsoil commonly found in higher latitudes, is starting to thaw in some places. According to a United Nations report, observations at two permafrost monitoring networks indicate that "large-scale thawing" may have already started.
What's next: That could have more serious consequences, as the frozen soil has trapped decomposed organic matter. As it warms, it could release more greenhouse gases, such as methane and carbon dioxide, speeding up climate change.
Declining polar bears
What's happening: Polar bears depend on the sea ice to hunt and seek mates. But as the ice disappears, bear mortality rises. In 2008, polar bears were the first animals to be added to the Endangered Species Act list of threatened species because of global warming.
What's next: With the chance that the Arctic could be entirely ice-free during the summer by 2030, the U.S. Geological Survey has warned that two-thirds of the world's polar bear population could be lost within 50 years as the sea ice continues to retreat.Â
What's happening: The latest research presented at the American College of Allergy, Asthma and Immunology in November showed that pollen counts are rising. Dr. Clifford Bassett, a New York allergist, explained that as the amount of carbon dioxide increases, some plants produce three to four times more pollen.
What's next: Pollen counts in the year 2000 averaged 8,455, but by 2040 that number is expected to rise to 21,735 ' an increase of more than 250 percent.
Fewer Monarch butterflies
What's happening: Scientists in Mexico found that monarch butterfly numbers dropped 59 percent this year to the lowest levels since record-keeping began 20 years ago. The decline could be due to increased wildfires caused in part by climate change, among other reasons.
What's next: Further decline could affect tourism in the Mexican state of Michoacan, where Monarch butterflies are a major attraction. Experts say it could also hurt plants and other species connected to the butterfly.
More severe droughts
What's happening: There have been increased periods of drought, particularly in famine-prone areas of Africa and Asia. The National Center for Atmospheric Research found that the percentage of Earth's surface suffering drought has more than doubled since the 1970s.
What's next: In Africa alone, the Intergovernmental Panel on Climate Change predicts that between 75 and 250 million people will be exposed to increased water stress due to climate change.