It is well known by now that climate change is real and human activities are the cause of climate change. The carbon dioxide concentration and Earth’s surface temperature is rising since industrialization in a mid-late 19th century. The rising temperature is causing melting of ice mass, sea level rise, increase in extreme weather events and changes in weather patterns. Scientists, researchers, and policymakers all over the world are working towards finding how much and how fast should we take action to address the adverse impacts of climate change? In this article, we elaborate on how do we know that climate change is real? We will focus only on the historical and current data to answer this question. We are also sharing links of videos showing a visualization of data providing evidence on climate change.
Historical Evidence on Climate Change
A change in climate is observed by monitoring weather variables, particularly temperature, over a long period. Historically, we got the first hint of global warming in 1938. An English engineer, Guy Stewart Callendar undertook a thorough and systematic effort to examine historical changes in Earth’s temperature. He took weather data from 147 weather stations around the world and initiated a massive international effort to standardize data from different countries and different years. After analyzing this data in detail, in 1938 he announced that the mean global temperature has risen by 0.5 degrees between 1890 and 1935.
The second line of evidence on climate change from direct measurement came in 1960. The role of CO2 in trapping the heat from sunlight was established in the mid-1850s. Scientists had calculated the expected change in Earth’s temperature due to a change in concentration of CO2 in the atmosphere. In 1958 Charles David Keeling began measuring CO2 with precision using the measuring instruments he developed himself. Within two years of data from Antarctica, in 1960, he reported that the level of CO2 is rising in the atmosphere. As the number of observations increased, the inexorable rise in CO2 concentration became evident. The other observatory established by Keeling in 1958 in Mauna Loa, Hawaii continues to be the most important source of data on CO2 concentration. The historical records of atmospheric concentration of CO2 are obtained from the analysis of the composition of air bubbles enclosed in ice cores from Greenland and Antarctica.
Current Evidence on Climate Change
The long-term data on carbon dioxide concentration and weather variables are freely available from various academic and research organizations. I have taken data from Earth System Research Laboratory, National Oceanic & Atmospheric Administration on CO2 concentration from 1958 to 2017. The highest historical CO2 level was less than 300 ppm, and it reached 406 ppm in 2017. The data shows that mean concentration of CO2 increased at the rate of 0.75 ppm/year during 1959-1968 and at the rate of 2.33 ppm/year during 2008-2017.
The rising concentration of carbon dioxide is changing the Earth’s temperature. Scientists report the rise in average temperature as a temperature anomaly as shown in the figure below. The graph shows the annual mean and 5-year running mean of the temperature anomaly in global mean surface temperature. This temperature is the average of temperature recorded at weather stations all over the world. There is a distinct rise in temperature from around 1910 till 1940. There is no variation from 1940 to the early 1970s followed by a steady increase. In 1940 to late 1960s, due to the change in the trend, there was confusion whether the climate was warming or cooling. Scientists explained that this was caused by blocked sunlight due to industrial pollution and was enhanced by long-term climatic oscillations and changes in Earth’s orbits. The warming trend resumed in 1975, and the scientific opinion started converging on global warming, not cooling. The increase in global mean surface temperature in 2017 is 0.9°C compared to the 1951-1980 average.
Visualization of Data on Climate Change
We have now an immense wealth of long-term data on weather variables. This data confirms that the climate is changing and it is changing very fast. There are more than 10,000 surface weather stations all over the world. Also, there are ships, weather radars, and satellites that gather precise data relevant to detect climate change and develop climate forecasts. Several international organizations are working tirelessly to assimilate and analyze this data. Following are the links to some of these visualizations:
- Earth’s temperature changes from 1880 to 2015 as a rolling 5-year average.
- Change in temperatures in different parts of the globe
- Changes in minimum Arctic sea ice (measured in September)
- Global ice viewer developed by NASA shows the changes in ice mass in Greenland, Iceland, Arctic, and The link has images of the glacier loss at several locations: https://climate.nasa.gov/interactives/global-ice-viewer/#/1/17
- The loss in Imja Glacier, Himalayas is seen in the images below.
- Visualisation of sea level rise caused due to the melting of ice mass and warming of oceans
The long-term weather data shows a clear and distinctive sign of climate change. The data on surface temperature, heat content of oceans, changes in ice mass and sea level height shows unprecedented changes. The visualization of this data not only gives the evidence but rings a loud alarming bell.