With apologies to Paul Revere, this post is on the lookout for cooler weather with an eye on both the Land and the Sea. UAH has updated their tlt (temperatures in lower troposphere) dataset for January. Previously I have done posts on their reading of ocean air temps as a prelude to updated records from HADSST3. This month I will add a separate graph of land air temps because the comparisons and contrasts are interesting as we contemplate possible cooling in coming months and years.
Presently sea surface temperatures (SST) are the best available indicator of heat content gained or lost from earth’s climate system. Enthalpy is the thermodynamic term for total heat content in a system, and humidity differences in air parcels affect enthalpy. Measuring water temperature directly avoids distorted impressions from air measurements. In addition, ocean covers 71% of the planet surface and thus dominates surface temperature estimates. Eventually we will likely have reliable means of recording water temperatures at depth.
Recently, Dr. Ole Humlum reported from his research that air temperatures lag 2-3 months behind changes in SST. He also observed that changes in CO2 atmospheric concentrations lag behind SST by 11-12 months. This latter point is addressed in a previous post Who to Blame for Rising CO2?
The February update to HadSST3 will appear later this month, but in the meantime we can look at lower troposphere temperatures (TLT) from UAHv6 which are already posted for February. The temperature record is derived from microwave sounding units (MSU) on board satellites like the one pictured above.
The UAH dataset includes temperature results for air above the oceans, and thus should be most comparable to the SSTs. There is the additional feature that ocean air temps avoid Urban Heat Islands (UHI). The graph below shows monthly anomalies for ocean temps since January 2015.
The anomalies over the entire ocean dropped to the same value, 0.12C in August (Tropics were 0.13C). Warming in previous months was erased, and September added very little warming back. In October and November NH and the Tropics rose, joined by SH. In December 2018 all regions cooled resulting in a global drop of nearly 0.1C. The upward bump in January in SH was reversed in February. Despite some warming in both NH and the Tropics, the Global anomaly cooled. The trajectory is not yet set, but soon we will see if the long-expected El Nino appears in NH and Tropics SSTs.
Land Air Temperatures Tracking Downward in Seesaw Pattern
We sometimes overlook that in climate temperature records, while the oceans are measured directly with SSTs, land temps are measured only indirectly. The land temperature records at surface stations record air temps at 2 meters above ground. UAH gives tlt anomalies for air over land separately from ocean air temps. The graph updated for February is below.
The greater volatility of the Land temperatures was evident earlier, but has calmed down recently. Also the NH dominates, having twice as much land area as SH. Note how global peaks mirror NH peaks. In December air over Tropics fell sharply, SH slightly, while the NH land surfaces rose, pulling up the Global anomaly for the month. In January both NH and SH cooled slightly, pulling the Global anomaly down despite some Tropical warming. Then in February, air temps over both NH and SH land rose, pulling the Global anomaly slightly upward to match 12/2018.
TLTs include mixing above the oceans and probably some influence from nearby more volatile land temps. Clearly NH and Global land temps have been dropping in a seesaw pattern, now more than 1C lower than the peak in 2016. TLT measures started the recent cooling later than SSTs from HadSST3, but are now showing the same pattern. It seems obvious that despite the three El Ninos, their warming has not persisted, and without them it would probably have cooled since 1995. Of course, the future has not yet been written.