How do we know climate change is real?

According to NASA there is unequivocal evidence that Earth is warming at an unprecedented rate, and human activity is the principal cause.

The evidence is presented in several categories, including these:

• Global temperature is rising;
• The ocean is getting warmer;
• The ice sheets are shrinking;
• Glaciers are retreating;
• Snow cover is decreasing;
• Sea level is rising;
• Arctic sea ice is declining;
• Extreme events are increasing in frequency;
• Ocean acidification is increasing.