which combination will produce a precipitate

And then there are the polar bears, long symbols of what could be lost in a warming world. Summers are becoming longer, and winters shorter - seasonal shifts that endanger countless animal and plant species by disrupting food supplies, mating seasons and other variables. Rising sea levels are threatening the beaches that sea turtles need for nesting. Carbon dioxide acts like a blanket in the atmosphere, trapping the sun’s heat and warming the planet.Ĭlimate change is already harming plant and animal life in ways that scientists are racing to understand. That number is now above 420 parts per million. Rather, scientists have found that the warming is best explained by rising concentrations of greenhouse gases in the atmosphere, put there by humans burning vast amounts of fossil fuels like coal, oil and gas since the start of the Industrial Revolution.įrom having studied bubbles of ancient air trapped in ice, scientists know that before 1750, the concentration of carbon dioxide in the atmosphere was roughly 280 parts per million. That’s especially true in the second half of the 20th century, when solar output actually declined and volcanoes had a cooling effect. The first three (solar energy, ocean patterns and volcanic activity) haven’t varied enough in the last 150 years to account for today’s rapidly rising temperatures. In studying the cause of today’s climate changes, scientists have looked at all of these factors. Volcanoes can have a cooling effect when they shoot out stuff that blocks solar radiation. The big ones are the sun (whose energy can fluctuate over time), ocean circulation patterns (which can change how heat is distributed around the planet), volcanic activity (which pumps material into the sky that can have either warming or cooling effects) and the overall amount of greenhouse gases in the atmosphere.Įach of these forces has played a role at different times in history.įor example, 56 million years ago, a giant burst of greenhouse gases from volcanoes or vast deposits of methane (or both) abruptly warmed the planet by at least 9 degrees Fahrenheit, triggering mass extinctions.Ībout 12,000 years ago, major changes in Atlantic Ocean circulation plunged the Northern Hemisphere into a frigid state.Īnd 300 years ago, a combination of reduced solar output and increased volcanic activity cooled parts of the planet enough that Londoners regularly ice-skated on the Thames River. Here’s how the science arrived at this place.įirst, it’s important to understand the main forces affecting climate.

One scientific study put it this way: The odds of current global warming occurring without human-caused greenhouse gas emissions are less than 1 in 100,000. They’ve reached an overwhelming consensus: The burning of fossil fuels by humans is the primary cause of global warming today.Įven scientists employed by oil companies have come to this conclusion. Over many decades, thousands of scientists have studied the warming planet. Read more: The Science of Climate Change Explained: Facts, Evidence and Proof Botanists see similar signs of the effects of climate change on crops, forests and other vegetation. Ornithologists, for instance, have shown that warming is affecting many bird species - changing when they nest, breed and migrate, and even where they are able to live and thrive. Scientists doing field research around the world have documented other effects of climate change. Rainfall data shows that heavy downpours have increased in the United States and elsewhere, because warmer air holds more moisture.Īnd not all of the evidence comes from instruments. Satellites that measure gravitational changes show that trillions of tons of ice have melted from the world’s ice sheets and glaciers.

Tide gauges and other instruments show that sea levels have risen by about half an inch per decade since 1900 (mostly because water expands as it warms). There is also plenty of evidence showing the consequences of this warming. The oceans have absorbed much of the heat trapped in the atmosphere. Temperatures in the top layer of the world’s oceans have increased as well. And the rate of warming has accelerated in recent decades.

On average, surface temperatures are 1.2 degrees Celsius (2.2 degrees Fahrenheit) warmer than a century and a half ago. The most basic measurements of temperature show that the world has been steadily getting warmer. This evidence is largely in the form of data from weather stations, buoys, ships, satellites and other sources. There’s overwhelming evidence that the world has been warming since the late 19th century, when the burning of fossil fuels became widespread and resulted in large-scale emissions of heat-trapping carbon dioxide into the atmosphere.

Which combination will produce a precipitate