Defining and Detecting Climate Change

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To provide reliable evidence for the existence of climate change, the world’s scientific community has developed sophisticated methods for detecting changes in the Earth’s atmospheric temperature, precipitation patterns, and the frequency and intensity of major storm events. To understand these methods, we must begin with a clear definition of climate change.

Inspired People

Hansen [photo]

James E. Hansen is one of the world’s leading climate scientists. In 1988, he was one of the first scientists to report that man-made greenhouse gases were heating up the planet. After 46 years in the U.S. National Aviation and Space Administration (NASA), he left in 2013 to become a full-time advocate for greater public awareness of global climate change. 1

Defining Climate Change

The Intergovernmental Panel on Climate Change (IPCC) is a collaborative group of thousands of the world’s top climate scientists from 195 different countries. In 1988, these scientists were asked by the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) to study and review climate data and climate models designed to describe the complicated interactions of the physical properties of our climate under different concentrations of GHGs.

The goal of the study requested in 1988 was to design climate change models that accurately reflect the real changes in our climate so that these models can be used to predict future changes of the Earth’s climate under different concentrations of GHG. Since the first completed report in 1990, the IPCC has produced comprehensive reports of climate change approximately every five years. These reports are used by government and United Nations leaders in developing policies addressing climate change. You can explore the IPCC website and access all reports.

Looking Ahead

In the upcoming Global Climate Change and Ethics section you will learn that the atmosphere is not only a natural, common property of Earth, but also a moral common good to be enjoyed by all human beings.

The IPCC defines climate change as “a change in the state of the climate that can be identified by changes in the mean and/or the variability of its properties, and that persists for an extended period, typically decades or longer.” Healing Earth uses this definition as its model for defining climate change.

A region’s climate is characterized by both the average and the extremes in its weather conditions, including temperature and precipitation. For example, evidence of climate change can clearly be identified in the trend of increasing temperatures over tens of thousands of years and in the increase in intensity and frequency of severe storm events. These changes are very different from normal day-to-day variations in the weather.

Detecting Climate Change

Global-scale scientific observations of the Earth’s climate system (including  measurements of temperature, precipitation, and other parameters) started in the mid-twentieth century. Modern observational techniques include both direct measurements on the ground and remote-sensing measurements from satellites (see Figure 5).

Figure 5: Scientific methods used to detect climate change; a. & b. rooftop weather stations, c. instruments attached to hot air balloons which rise high in the air and descend, making measurements throughout the flight, d. satellite photographs and measurements of storm events, e.—i. collection of ice cores for paleoclimate analysis of trapped air bubbles, and j. analysis of tree rings.1

For example, ancient climates (paleoclimates) can be reconstructed as far back as hundreds of thousands of years by studying atmospheric gases that have been trapped in ice core bubbles, and examining changes in deposition of seafloor sediments. More recent climates can be reconstructed by evaluating the growth rings of trees. These and other reliable detection methods provide a comprehensive view of changes in our climate over time. The temperature of our planet has experienced predictable cycles of warming and cooling throughout its history. These cycles have been identified as lasting 100,000 years each.

Figure 6. Vostok ice core record of temperature and carbon dioxide during the last 800,000 years.  The temperature scale is for warming and cooling in Antarctica and is reconstructed from analysis of stable isotopes in bubbles of air trapped in the core when this part of the ice core froze.1

The Vostok ice core study shows that these cycles of planetary warming and cooling are highly correlated with levels of carbon dioxide (CO2) and methane (CH4) in the atmosphere (Figure 6). Note the close relationship between CO2, CH4, and temperature.

Looking Ahead

Later in this chapter, you will learn how to measure your ‘carbon footprint’. From an ethical point of view, this is a measurement of how temperate you are in your use of fossil fuel.

It is believed that the glacial cycles (cycles of planetary cooling) are initiated by changes in Earth’s orbit around the sun and then amplified by concentrations of carbon dioxide and methane in the atmosphere through the greenhouse effect. However, variations in global climate, and increases in carbon dioxide and methane since the mid-eighteenth century have far exceeded the extreme ranges of these natural cycles. The large green and red arrows in the top right quadrant of Figure 6 show current levels of carbon dioxide and methane respectively, which are causing the extreme climate that the planet is experiencing today. You can also see present day increases by looking back to Figure 4, which provides a closer look at the increase in greenhouse gases over the last 2,000 years.

The IPCC commented on this phenomenon in 2013, stating: “Warming of the climate system is unequivocal, and since the 1950s, many of the current observed changes are unprecedented when compared to variations over the millennia. The atmosphere and oceans have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased.” It is important to remember that we are only in the beginning of a changing climate trend.