This year saw the release of three notable reports related to climate science. Together, they paint a clear picture:

• Global warming is largely caused by human actions,
• The future climate is likely to be very different without significant cuts in greenhouse gas emissions,
• Climate change impacts are already occurring, and
• Some future impacts could be catastrophic to communities, businesses and ecosystems.

The draft National Climate Assessment (NCA) was released for public comment in January, and the major conclusions aren’t expected to change when the final report is released in 2014. U.S. average temperature has increased by about 1.5°F since 1895 with 80 percent of this increase occurring since 1980. The report projects that temperatures will continue to rise, with a 2° to 4°F increase occurring in most areas over the next few decades. According to the report, these changes are contributing to an increased risk of extreme weather, coastal flooding, loss of biodiversity, and negative impacts on public health.

The Intergovernmental Panel on Climate Change Fifth Assessment Working Group 1 report (IPCC AR5 WG1), Climate Change 2013: The Physical Science Basis comes to many of the same conclusions as the NCA, but with a global focus. It represents an international consensus of governments on climate science and potential future warming. One of the key messages from this report was that the warming of the climate is “unequivocal,” affirming the IPCC’s comments from the Fourth Assessment in 2007. Many of the observed changes in the climate system since the 1950s are unprecedented over decades to millennia. These changes include warming in the atmosphere and oceans, reduced quantity of snow and ice, rising sea levels, and increased concentrations of greenhouse gases.

While scientific papers are published all the time, these two reports represent benchmarks, compiling recent scientific advancements to create an assessment of the state of climate science knowledge.

In addition to these comprehensive assessments, the National Research Council recently released a report, Abrupt Impacts of Climate Change: Anticipating Surprises, examining how abrupt climate change could have unpredictable, complex, and devastating consequences. In short, “abrupt changes” refer to significant shifts in physical, biological, or human systems that occur on a timescale of years to decades. They can occur without warning, faster than responses can be planned and carried out.

Scientists know that “tipping points” exist in the climate system, as we have evidence of their impacts in the distant past. But they are difficult to predict, and we may not be aware we’ve crossed a threshold until rapid, irreversible changes are already underway.

Abrupt changes are already happening such as the rapid decline of Arctic sea ice. Impacts of this loss could include erosion of vulnerable coastlines, disruptions of marine ecosystems, and shifts in Northern Hemisphere weather patterns.

Abrupt changes in the future could include a disruption of ocean circulation in the North Atlantic, which would change regional climate in many parts of the globe. In the Arctic, warming permafrost and ocean water could release large subsurface stores of frozen methane, which would then feed back into rapid warming of the Earth’s climate. The risk of some types of abrupt change is unknown, such as a sudden destabilization of large ice sheets in Antarctica that could cause sea levels to rise several times faster than today.

To deal with current and future threats, the report recommends creating an Early Warning System that would integrate and synthesize information from observations and models to better inform our monitoring, assessment, and management of risks.

While the United States had fewer headline-grabbing, billion-dollar weather disasters this year than last, and none on the scale of Hurricane Sandy, these scientific assessments remind us of the urgent need to take action to reduce emissions and prepare for the future impacts of climate change. Some businesses, governments, and communities are already taking leadership roles in reducing emissions and preparing for future impacts. These reports reinforce what climate scientists have been saying for two decades now—that human activity is the cause of climate change, and we must take action to reduce and prepare for future warming.