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April 19, 2018  |  Login
ecomii guides guide to global warming
In partnership with:  Union of Concerned Scientists

The weather, it is a-changin': How we know global warming is happening

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Scientists have been talking about global warming for decades, but not everyone was buying it. Some attributed the warming trend to natural climatic variations that have been occurring since the Ice Age. It’s true that the Earth’s weather has had its ups and downs, but today, scientists have compiled more evidence and have better climate science technology and methods to help us understand climate systems and patterns.

A simple way of remembering the difference between climate and weather is that ‘climate’ is what you expect (e.g., cold winters) and 'weather' is what you get (e.g., a blizzard). Weather refers to day-to-day changes like wind, temperature, humidity, atmospheric pressure, cloudiness, and precipitation. Climate refers to the average and variations in weather in a region over long periods of time.

Scientists have some ingenious ways of establishing climate patterns from centuries ago. They study tree rings, coral reef skeletons, and glacial ice cores. These studies have painted a clear picture: The past 10- to 20-year period was likely the warmest of the past millennium.

Recorded temperatures tell the same story. Data from the National Climate Data Center (NCDC), who has been keeping track of global average monthly and annual records of combined land and ocean surface temperatures since 1880, clearly show that nine of the top 10 warmest years globally have occurred since 1995. Today, the mainstream scientific community agrees that global warming is indeed happening.1

This documented rise in global temperatures isn’t the only proof that climate change is happening. There have been dramatic changes in the weather and in natural systems around the world that simply cannot be explained by natural causes. You may have even started to notice some of these changes: A certain flowering tree in your yard is blooming a little earlier each year, summer brings more intense storms or more heat waves, winter snowfall in typically snowy places is unpredictable or wetter. Witnessing these kinds of changes in the span of our lifetime is unprecedented.

What the experts say

But we also know global warming is happening because a UN-sponsored, international body of scientists known as the Intergovernmental Panel on Climate Change (IPCC) says so. Formed in 1988 by the United Nations Environment Programme and the World Meteorological Organization, the IPCC studies and synthesizes the latest scientific information from around the world on global warming and climate change. It is the most comprehensive and authoritative source of scientific information on global warming.

According to the Union of Concerned Scientists:-

“More than 1,250 authors and 2,500 scientific expert reviewers from more than 130 countries contributed to the [IPCC] panel's most recent report, Climate Change 2007: The Fourth Assessment Report. These scientists reviewed all the published and peer-reviewed scientific information produced during the previous few years to assess what is known about the global climate, why and how it changes, what it will mean for people and the environment, and what can be done about it. more

1. Union of Concerned Scientists (8 November 2006). [online] Available from: [15 November 2007]

2. Union of Concerned Scientists, (8 March 2007) [online] Excerpted from: [25 November 2007]

3. Union of Concerned Scientists, (8 March 2007). [online] Excerpted from: [15 November 2007]

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