But what happened before 1850?
A THREAD
A THREAD
Earth's climate has changed before for reasons nothing to do with human activity. Changes in the position of the continents, the sun's output, the number of volcanic eruptions, and the Earth's orbit have all influenced our planet's climate. Climate scientists study these reasons.
We know that none of those reasons can explain the warming measured since 1850. We also know that an increase in levels of greenhouse gases in the atmosphere will warm the planet, just as we've observed. It is our emissions of CO₂ that dominates recent warming trends.
We have enough thermometer observations of temperature to estimate changes in global average temperature since about 1850. We may be able to push that to about 1780 (work in progress - noc.ac.uk/news/new-proje…) but that's as far back as we can go with enough reliable data.
But, we also have lots of other exciting 'proxy' ways of measuring past temperatures, using trees, mud cores, ice cores, corals and other marine creatures, stalactites etc. This data allows us to estimate global temperatures for the last 2000 years: nature.com/articles/s4156…
Yes, the uncertainty in these estimates is larger than for recent thermometer data, but they still provide really useful context for recent changes.
The data shows a slow cooling trend up to around 1900, then a very sharp warming, consistent with our thermometer measurements.
The data shows a slow cooling trend up to around 1900, then a very sharp warming, consistent with our thermometer measurements.
So, we can now produce the #warmingstripes back to the year 1AD using reconstructions of global temperature from the proxy data, produced by PAGES2k, with the last 19 years provided by thermometer based estimates (HadCRUT4.6).
Context. #showyourstripes 
