Thread by @KHayhoe

This iconic graph tracks how rapidly our planet is warming. Yet every time it's shared on Twitter, someone always asks, "Why does it begin in 1850?"

The answer is simple: it's when we first had enough thermometers to compute a truly representative global temperature average.

The oldest continuous thermometer-based temperature record is Central England Temperature. It began in 1678 ... when Charles II was King of England! It shows how unusual today's warming is compared to the last four centuries of temperature variability. metoffice.gov.uk/hadobs/hadcet/

We can go further back via proxy records or "natural thermometers" such as historical records, bloom & harvest dates, pollen records, ice cores, etc. Against the backdrop of the last 2,000 years, today's warming is even more abrupt and unusual. Source: nature.com/articles/s4159…

Extending the temperature record back 12,000 years shows that today's warming is happening **more than 10 times faster** than the naturally-caused warming from the last glacial maximum to the peak of the Holocene, 6000 years ago.

That warming, 12,000 years ago, was driven by a factor scientists have understood quite well for over a century: Milankovic cycles. These are periodic variations in the earth's rotation and orbit that alter how and where sunlight falls on the earth. Read: climate.nasa.gov/news/2948/mila…

Could orbital cycles be causing our current warming? No; they should be causing us to very gradually cool in preparation for the next glacial maximum in about 1500 years. Instead, as this study concludes, we have "indefinitely postponed" the next ice age. people.clas.ufl.edu/jetc/files/Tze…

Using ice cores, we can track the history of heat-trapping gases and temperature back nearly a million years. They deliver a dire warning: as CO2 soars, so too does temperature; and we are already headed into conditions humans have NEVER experienced before.

As you see, temperature change lags CO2 - a bit. If we don't act soon, it will catch up all too quickly. Even worse, ice core data shows how natural feedbacks in the climate system amplify the impact of an initial warming, whether natural or human-caused. skepticalscience.com/co2-lags-tempe…

These records encompass the history of human civilization on this planet and even the existence of homo sapiens themselves. Looking further back, the planet has been warmer before. But it's **never warmed this quickly** and it's **never had 8 billion people on it when it did**.

Climate action isn't about "saving the planet"; Earth will endure. It's about saving US, us humans and the myriad of species we share this world with.
We're not fighting for a planet; we're fighting for a safe and sustainable home for us all.

And if you're wondering, yes - that is where the title of my book comes from! simonandschuster.com/books/Saving-U…

And for more on how we know the warming is not being caused by the sun, internal natural variability, volcanoes, chemtrails or planet Niribu, please see this thread:

https://twitter.com/KHayhoe/status/1032652591841386497