How do we know that climate is changing?

Well, climate has been changing all the time since our earth was formed some four and a half billion years back.

In the last one million years alone, there have been many significant changes in earth’s climate.

The current warming trend is yet another example of climate change.

Now, if you are one of those curious lot and are asking: “How are folks sure that the climate is changing now, and to what extent it is changing?,” here’s how: A whole range of technological advances have enabled scientists to see the big picture, collecting many different types of information about our planet and its climate on a global scale. This body of data, collected over many years, reveals the signals of a changing climate. Here are some data points from the information collected so far and their analyses:

• CO2 in the atmosphere – CO2 levels are the highest they have ever been in hundreds of millions of years.
• Global Mean Sea Level (GMSL) – Global sea level rose about 8 inches in the last century. The rate in the last two decades, however, is nearly double that of the last century.
• Land & Sea Surface Temperature – Global average temperatures have increased by 0.75 degrees C in the past 100 years, and about 0.5 degrees C in the past 40 years alone.
• Warming Oceans – The oceans have absorbed much of this increased heat, with the top 700 meters (about 2,300 feet) of ocean showing warming of about 0.3 degrees F since 1969.
• Shrinking Ice Sheets – The Greenland and Antarctic ice sheets have decreased in mass
• Glacial Retreat – Glaciers are retreating almost everywhere around the world — including in the Alps, Himalayas, Andes, Rockies, Alaska and Africa.
• Decreased Snow Cover – Satellite observations reveal that the amount of spring snow cover in the Northern Hemisphere has decreased over the past five decades and that the snow is melting earlier.
• Ocean Acidification – Since the beginning of the Industrial Revolution, the acidity of surface ocean waters has increased by about 30 percent. This increase is the result of humans emitting more carbon dioxide into the atmosphere and hence more being absorbed into the oceans.