The Earth reached a global warming milestone it may never recover from.<br />Climate scientists say carbon dioxide levels in the atmosphere surpassed 400 parts per million this month - 50 parts per million more than what most experts consider "safe."<br />And there's little hope that we will ever get our planet's levels back to that number again.<br />CO2 emissions have been a main source of climate change since the Industrial Revolution, causing Earth's temperature to rise 1.8 degrees Fahrenheit since then.<br />That's already led to record-breaking global temperatures, extreme weather and other effects.<br />Scientists are urging people to take this news as a wake-up call to get serious about reducing carbon emissions and fighting climate change.
