Natural changes in climate

0:00- [Narrator] Did you know that earth's climate hasn't always been the same? Sometimes it changes slowly over thousands to millions of years. Other times, a single natural event can change climate across the entire planet. In this video, let's learn how volcanic eruptions, meteorites, ocean currents, and even greenhouse gases have all influenced earth's climate.

0:22And we'll also see how scientists even figure this out. First of all, what is climate exactly? Isn't it the same as weather? No, it's not. Weather is the state of the atmosphere at a specific time and place. It describes the current conditions. For example, it can be sunny or it can be rainy, or snowy, or windy.

0:47Weather can also change from hour to hour. Climate, on the other hand, is a long term weather pattern in a specific area, usually measured across several decades. For example, a desert climate is usually hot and dry. A tropical climate is warm and rainy, and a polar one stays cold all year.

1:08So no, climate isn't the same as weather. It's the bigger picture. But even a single powerful natural event can disrupt it. For example, in 1815, a volcano named Mount Tambora erupted in Indonesia, one of the largest eruptions in the recorded history. It sent ash and gases like sulfur dioxide high into the atmosphere where winds spread these particles around the world.

1:38The sulfur dioxide formed a layer in the upper atmosphere that blocked some of the sunlight from reaching the earth's surface. With less sunlight, the Earth's surface cooled. In fact, the global temperature dropped by about two degrees Celsius. That's about 3.6 degrees Fahrenheit, enough to cause a major climate disruption.

1:59How major, you ask? Well, in the Northeastern United States and parts of Europe, snow fell in June, crops failed, and people faced food shortages. This event became known as, "The year without a summer." The climate effects actually lasted about three years, but this isn't the only eruption that has disrupted the climate.

2:22For example, more recently, the 1991 eruptions of the Mount Pinatubo Tubo in Philippines caused global cooling of about 0.5 degrees Celsius for nearly a year. So yes, volcanoes can cause changes in global climate, but it's not just the volcanoes. About 66 million years ago, a massive meteorite hit the earth near what is now Mexico's Yucatan Peninsula.

2:48The impact released huge clouds of dust and gases into the upper atmosphere, likely way more than Mount Tambora. Again, these particles blocked much of the incoming sunlight and scientists estimate that the effects of this meteorite reduced sunlight for up to 15 years.

3:06With less sunlight, photosynthesis slowed down or even stopped in many areas. As a result, many plants died. Without the plants, herbivores began to starve, which then affected the predators that relied on them. So food webs collapsed across ecosystems on both lands and in the ocean.

3:26This led to one of the Earth's largest mass extensions. About 75% of the species disappeared, including most of the dinosaurs. This wasn't just a local disaster, it was a global climate disruption triggered by sudden massive changes to the atmosphere. But guess what? It's not just the atmosphere.

3:46Earth's oceans also play a huge role in climate. Ocean currents move water and heat around the globe. This is part of a large system called the global ocean conveyor belt. Warm water flows from the equator towards the poles, and the cold water sinks and flows back again.

4:06For example, the Gulf Stream carries the warm water from the equator up to Europe through the Western Atlantic. This current helps keep Europe's climate relatively warm, but disruptions such as melting glaciers and ice sheets can weaken this current. And if that happens, the current could shift or slow down, causing Europe's climate to become colder.

4:30Then there's one more factor. Greenhouse gases. You probably heard of carbon dioxide, methane, or nitrous oxide, right? Well, these gases absorb and then re-emit heat from the Earth's surface, helping keep the planet warm. Greenhouse gases can come from natural sources.

4:49For example, volcanoes can also release carbon dioxide. Over thousands of years, repeated eruptions can add enough CO2 to the atmosphere to gradually warm earth's climate. Wetlands on the other hand, release methane and oceans can both store and release these gases depending on the temperature and the pressure.

5:08Over millions of years, changes in greenhouse gas levels have made the earth warmer or cooler. When the concentration goes up, earth warms, when the concentration goes down, earth cools. But wait a second, how do we know all this? Well, scientists have been able to reconstruct earth's past climate using a lot of different evidence from nature.

5:28For example, some scientists study ice cores from Antarctica and Greenland. The frozen layers of ice in these cores trap tiny bubbles of ancient air. And by analyzing the gases in these bubbles, scientists can measure past levels of carbon dioxide and estimate temperatures from hundreds to thousands of years ago.

5:51Scientists also study tree rings. Each year a tree grows a new ring of tissue under its bark. So the rings form a record of tree's life. In warm, wet years, trees grow thick rings. In the cold dry years, the rings are thinner. So by analyzing the pattern of the thick and thin rings, scientists can figure out what the climate was like year by year, going back hundreds or even thousands of years.

6:16So together this evidence shows earth's climate has changed over time due to natural events and processes. So this is how volcanoes, meteorites, ocean currents, and greenhouse gases can all influence Earth's climate.