by Science Buff
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How we know that climate change is real

Chapter 1 of 7

About this guide
There's overwhelming evidence supporting the claim that climate change is real. The intention of this guide is to list out all such known evidence.

There's a rising consensus in the scientific community that climate change is real and caused by human activity. 97% of climate scientists support this argument (more about this). 

People who deny climate change have their own motivations but once you look at the evidence, it helps in understanding the situation better and empowers you to educate others.

What this guide is not about

This guide is not about -
  • Countering arguments that skeptics may have against the evidence (we'll cover those in another guide).
  • How to stop global warming (deserves a dedicated guide of it's own).

Chapter 2 of 7

Evidence 1 : Increase in Carbon Dioxide levels.
Carbon dioxide is a greenhouse gas. This means it is heat trapping in nature and higher levels of it in the atmosphere would cause the planet to warm up more than it should.

The amount of carbon dioxide in the atmosphere has never been more than 300 parts per million in hundreds of thousands of years - until the mid of last century. Since 1950, this level has been crossed and it's growing linearly every year.

The direct measurement of the same, made since 2005 till now is represented in the following graph - 

How do we know what amount of Carbon dioxide was present in the atmosphere hundreds of thousands of years ago?

We do this by studying ice cores. These are cylinders of ice that has been freezing layer over layer for millennia. By studying the inner depths of the ice core, scientists can estimate what the atmosphere would have been like.

Learn more about ice cores here.
Data source here.

Chapter 3 of 7

Evidence 2 : Rising Sea Level
If global warming is really happening, it would lead to to -
  1. Melting of glaciers and ice sheets.
  2. The oceans to swell up (expand).
This should in turn cause the sea levels to rise. Guess what? Global sea levels are indeed rising!

The following graph shows the rise in sea height variation from 1993 to the present year
And following is another graph showing the change in sea level through the last century 1870-2000.

Chapter 4 of 7

Evidence 3 : Rise in Global Surface Temperature
Global warming causes Earth's overall surface temperature to rise over time. There's statistical evidence that Earth's surface temperature has significantly risen through the last century.

Here's a graph showing the rise in temperature anomaly from 1880 to 2016 -

This evidence is super compelling because all 17 years since the year 2000 have been the warmest with respect to the previous year.

To visualise how bad this has been, here's a 20-second time lapse video of how surface temperature has risen from 1880 to 2016 -

Data source here.
Learn more about how human activity has caused the global surface temperature to rise here.

Chapter 5 of 7

Evidence 4 : Shrinking Ice Sheets
The rapid increase in temperature has also resulted in melting of the Antarctic and Greenland ice sheets.

The following graph shows the loss of antarctic ice sheet mass since 2002. It's decreasing at an avg. of 125 gigatonnes per year - 
Greenland ice sheets are decreasing in mass at the rate of 287 gigatonnes per year - 
Data source here.
To learn more about how ice sheets are loosing mass across the world, check out Global Ice Viewer.

Chapter 6 of 7

Evidence 5 : Arctic Sea Ice
Measurements show that the arctic sea ice is melting rapidly since late last century.

Arctic ice melts every year and reaches to it's lowest point in the month of September. Here's a graph showing how we're reaching a new low every September, decade after decade - 
And here's a quick video to visualise the above graph - 

 Data source here.

Chapter 7 of 7

Other evidence
Apart from specific data backed evidence, there are many other compelling signs indicating that climate change is real. Here's a list of those - 

Decreasing Snow Cover

The northern hemisphere is loosing snow cover rapidly since the last five decades. Learn more here.

Ocean Acidification

Measurements suggest that the surface oceans have become 30 percent more acidic since the mid of last century (industrial revolution). This is a great threat for the aquatic ecosystem. Learn more here.

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