Meanwhile, observations over the last 40 years indicate with high confidence that increased heat in the oceans, as well as glacier loss in areas such as Greenland, account for the overwhelming majority of sea level rise. Indeed, the impact of human-driven warming is widespread— in the ocean, in changes to the global water cycle, in reductions in snow and ice, in sea level rise and in many extreme weather events.4) Without Action, Things Are Poised to Worsen.What we have witnessed to date is only a small taste of what is in store if emissions continue unabated. Scientists have found:It is virtually certain there will be more frequent hot and fewer cold extremes in temperature over the majority of land areas. Heat waves will very likely occur with higher frequency and last longer. The western United States, and especially the Southwest, is expected to become drier. The ocean is becoming so acidic so quickly, it is unclear whether and how ocean life can adapt. Livestock and fish production are expected to decline, as are many crop yields as a result of altered rainfall, extreme weather and increased pests.A Time for ActionIt is overwhelmingly clear that if human beings continue to burn fossil fuels, cut down their forests, and build high-carbon and inefficient buildings, among other activities that spew greenhouse gases into the atmosphere, it will produce a climate that our planet has not seen since before human civilization emerged.Although we can’t predict with exact precision how climate change impacts will unfold, that doesn’t mean we don’t have more than enough information to take action. Most of us take reasonable precautions and purchase insurance for fires or floods to reduce risks in our own lives. We certainly expect the government to protect us against societal threats—whether they are related to national security or pandemics—even when information is not perfect. So, too, we need the government to continue to set policies that will make people, infrastructure and businesses safer from the threat of climate change.Science also tells us this: We can avoid the worst risks of climate change by cutting emissions and moving to a low-carbon economy. We expect those charged with protecting human health and the environment to face facts. The truth is that the threat is far too grave to ignore. This post is part of WRI’s blog series, The Trump Administration. The series analyzes policies and actions by the administration and their implications for climate change, energy, economics and more.During the recent confirmation hearings of President Trump’s cabinet nominees, a familiar pattern has emerged. Many of them have acknowledged that climate change is happening, but each has then sowed doubt by either understating the connection between human activity and climate change or by suggesting that there’s too much uncertainty to act. The overall effect of these statements is to confuse or stall progress.The reality is that we know plenty about the role of people as a primary driver of climate change, and government officials certainly know more than enough to act.For example, during his hearing to become the EPA administrator, Scott Pruitt claimed: “There is a diverse range of views regarding the key drivers of our changing climate among scientists.”Rex Tillerson, President Trump’s selection to become the next Secretary of State, remarked: “I agree with the consensus view that combustion of fossil fuels is a leading cause for increased concentrations of greenhouse gases in the atmosphere. I understand these gases to be a factor in rising temperatures, but I do not believe the scientific consensus supports their characterization as the ‘key’ factor.”Simply put, these views are not accurate and fly in the face of well-established science. The underlying research showing the connection between increasing CO2 concentrations and a warming planet was established more than 150 years ago. The statements above conflict with conclusions from all leading national and international scientific institutions (IPCC, NCA, WMO, NAS and UK MET Office), and they contradict the findings of the departments and agencies these appointees may soon be leading.It is time for these leaders to look carefully at the climate science and establish policies based on the best scientific information available.Here’s a brief reminder of some of our fundamental understanding about climate science:1) Global Temperatures Are Rising at Unprecedented Levels.2016 was the third consecutive year of record-warm global average temperatures. 16 of the 17 warmest years on record have occurred this century. Average global temperatures have been above the 20th-century average for the past 40 consecutive years. Since 1880, global temperatures have risen by more than 1˚C (1.8˚F), while levels of carbon dioxide in the atmosphere have increased from 280 parts per million (ppm) to more than 400ppm. 2) As Global Temperatures Rise, Extreme Weather Events Are Becoming More Frequent and Severe.As the atmosphere and ocean warm, they provide additional energy for extreme weather to tap into. For example, warmer temperatures allow the atmosphere to hold more moisture, which can drive heavier downpours. Melting land-based ice combined with warming oceans fuels global sea level rise, which amplifies storm surge and coastal flooding:Coastal flooding from high tides has increased by 364 percent to 925 percent in locations on all three U.S. coasts over the last 50 years. Heavy precipitation events have increased in every region of the contiguous United States since the late 1950s. The record rainfall that devastated Louisiana last August was one of six 1-in-1,000 year rainfall events that occurred in the United States last year. The deluge caused $10 billion in damages while inundating the state with more than 7 trillion gallons of water (3 times as much rain as the state received during Hurricane Katrina). Scientists found it to be 40 percent more likely to occur today than in 1900 as a result of climate change. 15 extreme weather events each costing $1 billion or more occurred in the United States in 2016, causing $46 billion in aggregate damages. Even when adjusting for inflation, four of the five years with the most billion-dollar extreme weather events in the United States have occurred since 2010.3) Human Activity is the Main Cause of Climate Change.Scientists have determined that it is extremely likely that the increase in greenhouse gas emissions from human activity has caused more than half of the observed increase in temperature over the last 60 years, making it the largest driver of climate change.When models only include natural drivers of climate change, such as natural variability and volcanic eruptions, they cannot reproduce the recent increase in temperature. Only when models include the increase in greenhouse gas emissions due to human activities can they replicate the observed changes.