Empirical evidence review: It has now been 30 years since the former chief NASA climate scientist, James Hansen, unleashed his climate apocalypse scenarios on the public in 1988 ... looking back, does the empirical evidence support the fears of "unprecedented" warming?
It has long been common knowledge among both scientists and laypeople that the world has been warming since the Little Ice Age (LIA) ended during the mid-1800s. In fact, from January 1850 through January 1988, the world had already warmed over 1 degree Celsius.
And it was in 1988 that James Hansen decided to present the case that this slow warming since the LIA was soon to become "unprecedented" due to CO2 emissions, thus causing untold climate chaos - i.e. boiling oceans, droughts, famines, Manhattan Island flooding along with other coastal regions, Earth turning into the next Venus, and etc.
Factually, the world has continued to warm since 1988, but is it "unprecedented" versus the climate warming of pre-1988?
It's not enough simply to claim the world is warmer, more important is to determine if temperatures changes are larger than ever.
To determine if today's global warming deserves to be considered unprecedented, an analysis of 30-year (360-month) climate temperature changes would be an effective means.
Using the gold-standard surface temperature record dataset, the HadCRUT4.6 global anomalies stretch back all the way to 1850.
We know from that dataset that the modern 30-year climate temperature change was +0.29ºC of warming at the end of February 2018. To clarify, that is the temperature warming change from February 1988 through February 2018.
That +0.29°C temperature since 1988 change took place in a global climate context that included not only the impact of multiple powerful El Niños, but also an atmosphere that was infused from 1989-2016 with over 50% of the total human CO2 emissions (metric tonnes) emitted since 1850.
Yet, despite all those CO2 emissions over the last 30 years, as the adjacent table reveals, there are 28 previous 30-year changes all ending in the month of February that exceed the "unprecedented" the most +0.29°C change.
All 28 of those 30-year temperature changes took place before the additional 50% of all CO2 emissions were released into the atmosphere.
By expanding the analysis to include all 12 months - not just the month February alone - there have been 247 monthly instances prior to 1988 when long-term the 30-year global temperature warming change exceeded that for February 2018.
In contrast to the above, the 30-year change in CO2 ppm as of February 2018 significantly exceeds all 30-year CO2 changes prior to 1988 without fail.
As an aside, in regards to the short-term, the 12-month global temperature change was a minus -0.32°C for the month-end of February 2018.
Conclusions:
True: The world has warmed since 1988 as the global temperature dataset establishes.
But, per the same empirical evidence, the current modern warming, as represented by 30-year temperature increases, is not in the least extreme, unusual, or unprecedented.
Prior to the additional 50% of total metric tonnes of CO2 emissions being added to the world's biosphere, global warming change easily matched or exceeded that experienced since 1988 - the year of NASA's James Hansen's predictions of climate apocalypse from human CO2.
Based on all the the gold-standard temperature measurements that the HadCRUT dataset provides, it is evident that periods of exceptional global warming changes (and the recent cooling temp changes) are more likely driven by natural forces than the ever-increasing levels of atmospheric CO2.
Note: Excel used to calculate 30-year temperature changes from the HadCRUT global land/sea dataset of temperature anomalies and past CO2 data (links found here). Left column of table are months of February and associated year; right column of table are the 30-year changes in temperature anomalies. Only chose to show the sub-list of February examples instead of all months, which was comprised of 247 in total.