Editor’s note: This is the first in a series of short articles about various aspects of climate change. No single article is designed to address this topic in its totality nor is “Outdoor America” attempting to cover every conceivable climate-related issue. The goals of the series are to communicate the fundamental facts and address issues most relevant to the League’s mission.

If the worst team in your favorite sport won a single game, you probably wouldn’t bet on them to win next year’s championship. But, if they began taking the title season after season, putting your money on that team might start to seem like a good idea.

We all understand that a team’s performance in any one game is not the same as its record during several seasons. This difference is like the difference between weather and climate: weather is today; climate is a pattern. The same way that one big win doesn’t mean a team has improved, one very hot day doesn’t mean the climate is warmer.

But when winning streaks and heat waves come more often and last longer, and when we see this pattern continuing through the years, then we can say that something really has changed. This is what scientists mean when they talk about climate change.

We all know that weather changes all the time. Climate, on the other hand, is a predictable pattern that tells us the range of weather we can expect and how often we might see weather at the extremities of that range.

Climate scientists, and many governments, agree that we must hold atmospheric carbon to less than 430 ppm in order to preserve a safe climate – but right now, we’re on track to smash through that limit by 2028.

Climate is inherently a long-term concept. In order to say that the climate, and not just the weather, has changed, we need long-term data. Through careful study of evidence hidden in tree rings, ice cores, ocean sediments, and the observable movements of our planet, scientists have painstakingly collected that data. Thanks to their work, we know what the average temperatures on Earth have been for the past tens of millions of years. That data is showing us that while our planet has warmed before, the speed and scale of the current warming is unlike any historical warming pattern.

In addition to knowing how global temperatures have changed historically, and how they’re changing now, we certainly want to know what causes these changes. The data collected by scientists tells us that too. By investigating geological layers left behind by volcanic eruptions, air bubbles trapped in ancient glaciers, and the cycles of solar activity, scientists can analyze factors that influence our planet’s climate and see which factors line up most closely with temperature variation in the past – and with the temperature variation we’re seeing today.

Climate scientists have been carefully studying this data for decades, and now 97% of them agree: our planet is getting warmer and it’s because of people.

The Intergovernmental Panel on Climate Change (IPCC), comprising thousands of climate scientists from around the world, overwhelmingly agrees that atmospheric concentrations of greenhouse gases – such as carbon dioxide, methane, and nitrous oxide – are higher than they’ve been at any other point during the past 800,000 years. IPCC is highly confident that these emissions are coming almost entirely from human activity, not from natural sources.

In 2015, the U.S. Environmental Protection Agency (EPA) reported that atmospheric concentrations of carbon dioxide stood at 401 parts per million (ppm), a 43% increase over the annual average of 280 ppm in the late 1700s. According to climate.gov, this total has been rising by 2.3 ppm per year during the past decade, as opposed to 0.6 ppm per year in the 1960s. Climate scientists, and many governments, agree that we must hold atmospheric carbon to less than 430 ppm in order to preserve a safe climate – but right now, we’re on track to smash through that limit by 2028.

This accelerating increase in atmospheric greenhouse gases tracks a similar speeding-up of human emissions. In 1900, humans were emitting 2 billion metric tons of carbon dioxide per year, according to a report from Our World in Data. That figure had increased to 36 billion metric tons annually in 2015. And much of this increase has come in recent years: EPA reports that worldwide emissions in 2010 were 35% higher than those in 1990.

Climate change is happening, it is caused by human activities, and we are seeing the impacts of it now.

We see the same upward trend in average global temperatures. This important fact demonstrates how temperatures, greenhouse gases, and human emissions are interrelated. In 2015, eminent climate scientist James Hansen reported that the average temperature of the Earth is higher now than it has been at almost any other time in the past 800,000 years. Since 2015, the average global temperature has continued to trend steadily upward. This sustained shift in temperatures – across all seasons, all parts of the world, and across a span of many years – is exactly what is meant by climate change.

Climate change itself may be hard to see, but the evidence is clear and the physical warnings are becoming more prevalent. The fingerprints of this dangerous shift are all around us. The higher average temperatures are manifesting in the increasing frequency of high-temperature weather events we call heat waves. The warmer air is also holding more moisture, which causes heavier rainfall and contributes to inland flooding.

Much of the excess heat is going into the ocean, where higher water temperatures provide the energy that powers stronger hurricanes. Water expands as it warms, therefore sea levels are rising faster than they did in past centuries, contributing to flooding of coastal cities even on sunny days.

Scientists have been nearly unanimous for years, and members of the public increasingly agree: Climate change is happening, it is caused by human activities, and we are seeing the impacts of it now. In upcoming issues of “Outdoor America,” we will explore some of these impacts on public health, our economy, and natural resources. We’ll also take a deeper look at the policies League members voted to adopt, how League staff are taking action on those policies, and how you can get involved.

Learn more about climate science and solutions