Friday, 29 September 2017

August, 2017 second hottest despite la-NIna

With Indicators Pointing Toward Back-to-Back La Ninas, NASA Shows August 2017 was Second Hottest on Record

28 Sepetember, 2017

The Earth really hasn’t backed off that much from the record heat of 2016. And since we’re experiencing what NOAA states is more and more likely to be back-to-back La Nina periods, the world should really sit up and take notice.

El Nino and La Nina Variability as Part of the Larger Warming Trend

As a measure of natural variability, La Ninas bring cooler conditions to a large portion of the Equatorial Pacific Ocean. Since the influence of this ocean on the larger climate system is so strong, La Ninas tend to generate periodic cooling in surface temperatures across the globe.El Nino, by contrast, generates periodic warming. The cycling between these two states can be imagined as a wave form.

(1998 and 2016 were both strong El Nino years — producing new record hot global temperatures when they occurred. Follow-on La Nina years resulted in counter-trend cooling that was not great enough to disturb the much larger overall global warming based trend. Image source: NASA.)

This cycle, however, should not be confused with the overall larger climate trend — which has been for considerable and rapid warming over the course of more than a century. That said, and despite the larger and obvious warming trend, La Nina years have tended to be cooler than El Nino years. This prevalence has resulted in years in which global surface temperatures temporarily, but slightly compared to the larger trend, back off from recent records. Meanwhile, El Nino years have tended to bring on new record hot temperatures due to their peaking influence on the greater trend of fossil fuel and carbon emissions based warming.
August 2017 Second Hottest on Record; 2017 Also Tracking Toward Second Hottest Year

According to NASA, August of 2017 came in as the second hottest August in the 137 year climate record. Overall August temperatures were 1.09 C warmer than 1880s averages. A measure that came in 0.14 C cooler than the record hot August of 2016 and 0.05 C warmer than the third hottest August — 2014. This added heat to the Earth System continued a larger record trend that has been in place at least since 2014 in which temperatures near the Earth’s surface spiked to far higher than previous levels (see image above).

Present NASA tracking shows that the first 9 months of climate year 2017 (Dec-Aug) were 1.14 C hotter than 1880s averages. By comparison, climate year of 2016 (Dec-Nov) hit 1.24 C above 1880s averages with January through December hitting 1.22 C above 1880s averages. The third warmest year on record, 2015, came in at around 1.09 C hotter than 1880s. Given this larger trend, NASA scientists presently provide an 83 percent probability that 2017 will come in as the second hottest year on record.

Back to Back La Ninas Probably on the Way, But no Significant Cool-Off So Far
It appears that 2017 is likely to hit around 1.11 C above 1880s averages. This is a 0.11 C dip below the record hot year of 2016. And it’s a dip enabled by the formation of a La Nina during fall of 2016 and a likely back to back formation of La Nina during the same season of 2017. In contrast, the strong La Nina following the 1997-1998 El Nino produced a much greater relative global temperature drop of around 0.2 C. An approximate 0.1 C return from the very strong 2016 spike is not much of a variability-based fall back and could point toward a stronger relative warming and a possible near term challenge to the 2016 global record in a likely El Nino during 2018-2020.

(One of the sole cooler than 30-year climatology regions in the Pacific is the Equatorial zone stretching from the Central Pacific to the West Coast of South America. Periodic cool water upwelling is driving this cooling which is a signal for La Nina. NOAA presently identifies a 55 to 60 percent chance of La Nina developing during fall of 2017. If this happens, late 2016 and late 2017 will feature back to back La Ninas. Despite this development, global temperatures are still hanging near record hot ranges. Image source: NOAA.)

Wild cards for this fall will hinge, in part, on how strong Northern Hemisphere polar amplification ramps up as Arctic cooling lags. Arctic sea ice extent appears to be tracking toward 5th to 6th lowest on record at end of the summer melt seasonWhile sea ice volume has hit near second to fourth lowest on record. Both re-radiated heat from warmer than normal Arctic Ocean sea surfaces and larger energy transfer from the middle latitudes should drive a strong polar amplification signal similar to those seen during recent years. And, already, it appears the upper latitude Northern Hemisphere cooling is lagging typical 30-year climatology. However, it remains to be seen whether fall of 2017 will rival fall of 2016’s record observed heat transfer over the Pacific and north into the Beaufort region.

Such a signal would likely firmly solidify 2017 as second hottest on record. However, stronger than expected variable La Nina based cooling could upset this trend and bring 2017 closer to 2015 values. With so many months already passed, we’re looking at a possible swing of 0.02 to 0.04 C on the lower end if La Nina is stronger and a strong polar amplification signal does not emerge — which would still result in less of a variable dip than we saw post 1998.
(High amplitude Jet Stream waves to again transfer prodigious volumes of heat into the Arctic during fall of 2017? Watch this space. Earth Nullschool GFS model based image from September 28, 2017 shows another larger ridge forming over the Pacific Northwest and extending up into the Arctic.)

The end result is that the world is now firmly in a 1 to 1.2 C above 1880s temperature zone. Such a zone is one that is well outside of typical recent human experience. One that will tend to continue to produce unsettling and harmful weather and climate extremes. Furthermore, increasingly harmful climate change related events are likely to more swiftly ramp up with each additional 0.1 C in global temperature increase and as the world approaches the 1.5 C to 2 C threshold.

No comments:

Post a Comment