Did We Just Blow Past the 2˚ “Limit” for Global Warming?
The web has been awash with reports highlighting the truly shocking global warming figures recently released by NASA and NOAA.
These announcements have led some to argue that we have already blown past the ideal warming limit of 1.5˚ agreed upon last December in the Paris Climate Agreement, and that we may have even breached the hard 2˚ limit.
The numbers from NASA and NOAA should wake up anyone still sleeping on threat posed by keeping on with our fossil fueled ways. But the numbers don’t, in fact, say game over.
NASA reported that February’s monthly temperature was 1.35°C above the 1951–1980 global average for February. This represents the largest departure from the average for any month in recorded history.
And the February temperature was 1.65˚C above the “pre-industrial” era baseline used to set the 2˚C goal adopted in Paris.
However, over the course of a full year, the temperature rise for all of 2016 will likely be much closer to 1.0˚ than the monthly departure of 1.65˚ recorded in February.
The Japan Meteorological Agency (JMA) reports against a baseline of 1981–2010, a much more recent, and hotter baseline. But from the agency’s graph you can see how the anomaly (i.e. the departure from average) in February 2016 compares with the temperature anomalies of Februaries past.
The data for February is only a snapshot in time. It does not represent the yearly average by which the effort to curb global warming is measured. Monthly variations during the year can be quite large, especially during an extreme El Niño event. See JMA graph to get a sense of this variation. Over the course of a year monthly variations in both directions tend to cancel each other, leaving only the average trend.
The final yearly number for warming in 2016 will almost certainly clock in far lower than the monthly February number. El Niño is already fading, and predictions suggest that La Niña will bring cooler than average temperatures in the fall. While it is increasingly likely that 2016 will beat the record for global warming set in 2015, it’s not going to rise above the ideal 1.5˚ limit, much less the hard 2˚ limit.
What About Adjusting for Warming Since “Pre-Industrial?”
The call to limit global warming to 2˚C in the Paris agreement was adopted under United Nations Framework Convention on Climate Change (UNFCCC), and it is referenced against “pre-industrial levels.” Unfortunately, the exact date of “pre-industrial” has never been defined by UNFCCC.
The 2˚goal, the 1.5˚ stretch goal, and the emissions reduction commitments towards those goals, were adopted by world leaders in the 2015 UNFCCC session in Paris where the IPCC AR5 report served as the formal science input to the negotiations.
The IPCC AR5 report explicitly references the temperature baseline of 1850–1900 in the modeling scenarios that were used to set UNFCCC emission reduction policies (see Table TS.1 in the AR5 WGI Technical Summary). And the carbon budget discussed in the IPCC WGI Summary for Policy Makers is presented for the purpose of “Limiting warming… to less than 2˚ C since the period 1861–1880.”
To adjust NASA numbers against a baseline in the late 1800’s, former NASA climate center director Jim Hansen has calculated that an adjustment of +0.3˚C should be made.
Thus the global temperature in February 2016 was 1.65˚ warmer than the the Februrary temperature in the pre-industrial period defined as the late 1800’s.
Some argue for adding 0.6˚C to the NASA figures to account for warming back to 1750, a time frame spanning many decades, during which significantly different, non-industrial human activities dominated global warming. However, the 2˚ goal and the 1.5˚ stretch goal were not established against that time frame.
The original choice to measure global warming against a baseline of the late 1880’s was taken in part because good instrument temperature readings only go back as far as 1850, while even more reliable instrument readings are only available since the late 1800’s. To go back further than 1850 requires considerable use of temperature proxy records (e.g. tree ring records) which have become more available and reliable only in recent years.
Of course science has also recently shown that even 2˚ of warming since the late 1800’s is extremely dangerous. A limit of 2˚ is no longer seen as a guard rail, but rather as a last ditch defense line. Nevertheless the 2˚ goal, as measured against a late 1800’s baseline, is the goal to which nations committed themselves in Paris, along with the 1.5˚ stretch goal.
While there can be merit in taking a literal view of the term pre-industrial and in looking all the way back to 1750, adopting that view would not be appropriate in discussions regarding the progress toward limiting warming below the 1.5˚ and 2˚ limits set in Paris.
So what does this all mean?
The monthly temperature in February was 1.65˚C above the “pre-industrial” baseline used by UNFCCC to set the 2˚C goal.
The average warming for all of 2016 will likely end up being slightly above the 1.0˚ C warming seen in 2015, continuing a dangerous trend.
We have not blown past the 1.5˚C goal, yet.