TheClimateChanger

Interesting. Wonder if there is any chance for a late Beaufort melt to gain some ground? Delayed, but not denied, as JB would say.

Evening notes:

It looks like your analysis suffers from some unfounded assumptions. I don't see any evidence that "the land masses in the NH ... likely had a negative greenhouse effect" during the LGM. Looks like this phenomenon is quite rare - limited to the Antarctic Plateau - and seasonal (no negative GHE in austral summer). Much of Antarctica does not have a Negative GHE, as per Figure 1 in the paper cited. And that appears to be the case for Greenland as well. They do surmise that perhaps such conditions occurred in past ice ages, but only specifically identify Greenland as a possibility. I think it's unlikely the continental ice sheets (e.g., Laurentide) would have been sufficiently devoid of water vapor and subject to the same intensity of inversion as the Antarctica Plateau. But even if they did, I don't see how this calls into question the role of CO2? CO2 would only be a negative feedback if a true negative GHE existed; even with a weaker positive GHE, it would still be a positive feedback. Moreover, it would be a positive feedback everywhere not covered by ice even assuming a negative effect over ice. As you, yourself, have previously pointed out, warming in one location does not exist in a vacuum. Ocean and atmospheric currents would eventually move warmer air across the globe. Over time, warming of the unglaciated regions would increase water vapor and erode the surface temperature inversions over the glaciated regions, shifting any negative GHE to a positive one. The cited paper suggests the same could occur over Antarctica:

See, I've got pretty good company here. Hansen is more than a little skeptical of what the IPCC says, suggesting a climate sensitivity much higher than supposed (4.5C v. 3C).

Today will be the 9th consecutive day without measurable rainfall at the airport, assuming nothing pops up (there were a few scattered showers earlier north). Only 0.39" over the past 21 days.

Interesting temperature pattern yesterday in the northeast. Map below shows yesterday's high temperature percentile. Much of the interior decidedly above the median high temperature - generally 70 to 85 percentile. Buffalo was only a few degrees shy of a record, topping out at 89F as an odd easterly flow brought some downsloping sending the warmest temperatures to the lakeshore (typically cooler locations). The coastal Plain was pretty close to the median - generally from about the 33rd to 67th percentile, except for Boston, which didn't make it out of the low 70s. The ASOS at Logan is very close to the water. Big divergence from BOS to Blue Hill Observatory (Milton, Mass.) just to the south. Cooler high temperatures in West Virginia from clouds and showers.

Summer ain't over yet!

Today's thread:

In a stunning departure from the conditions of the summer to date, August has started off on a very cool note nationwide. The PRISM data below is only for the first two days of the month, but yesterday saw similarly impressive cold with a number of record low max temperatures in the south and a few isolated record lows in the eastern US. While I still expect August to finish out above normal for CONUS, this is going to make a new summer national record quite difficult. Will probably take a few days just to return to 1991-2020 means nationally, which means we are likely looking at one of the coolest first weeks of August in a long while. Probably would need an epic heat wave to keep pace with 2021 & 1936, at this point.

Beautiful stretch. At PIT, we've doubled our July tally of low temperatures below 60F in the first four days of the month. Happy I've been able to give the A/C a rest for a change.

Wow, I don't agree with this statement at all. Recent Julys have had mean minimum temperatures that are warmer than the mean 24-hour averages from past "cold" Julys. Probably after 2050, we will begin to see Julys where the mean minimum temperatures exceed the mean maximum temperatures from old-school cold Julys. For some reason, you only ever look and compare to the hottest years? For example, JFK's mean minimum last month was 72.7F. That exceeds the mean 24-hour average of 71.8F in 1956, 72.2F in 1996, 72.2F in 1965, 72.3F in 2000, 72.4F in 2001, and falls just shy of the 72.8F observed in 1976. It's probably just a handful of decades before JFK starts seeing low temperatures in July that exceed the mean maximum temperatures observed in cold Julys (e.g., 1956, 77.9F; 1996, 78.6F; 2000, 79.5F; and 1967, 79.7F). I don't think its too hard to imagine a future in 2060 where NYC looks more like Washington, DC of 2000-2020, where such low temperatures are common. I think it's significant when low temperatures are exceeding the mean of high and low from many past years. In the first 6 years after installation of the ASOS at JFK, there were 3 years in which the month of July had a colder mean temperature than this year's mean low temperature (1996, 2000, and 2001).

"It's only summer." Just kidding. Actually, the weather today and this weekend is closer to "only summer" weather than the past 6 weeks. The mean minimum temperature of 68.2F at PIT last month was 0.8F higher than the mean average (avg. of max & min) temperature from 1976, and pretty comparable to the mean average temperature observed in 1960, 1984 & 2000.

You can even see the point where atmospheric changes start to swamp out the UHI signal. From 1970-2000, both sites show a small cooling trend, with NYC lows dropping 0.2F, while the Charlotteburg site saw lows drop by 0.7F during that timeframe. Hard to tell if the late 20th century cooling is a real trend or just an artifact from changing equipment/observation practices and site location. I'm not sure if that cooling trend is real or just manufactured by those non-climatic factors.

Wow, since 1970, July nighttime low temperatures at NYC have risen 3.1F, while lows at Charlotteburg Reservoir have risen 7.1F, per linear regression.

I mean not every month is just going to continue being cooler than the corresponding month in 2024. Eventually that trend has to stop, no? Maybe in time for December, which was about a degree cooler than normal in 2024.

Last year was record warm only for the period 1869-2024. For the period 2025+, it will be considered a cool year.

2007 also had crazy heat in the south and Ohio Valley. I don't think summer is over yet.

Analogs seem good for some big heat. I see 1953, a couple from 1988, 2001 (big heat in early August), 2002.

That rubber band is going to snap in a BIG way soon, I would imagine.

Good post, Tip. I expect Massachusetts to finish around 73.7F for the month (+/- 0.3F). Very crowded field. That figure would place them in ninth, but just an extra tenth would move 2025 instead to a 4-way tie for 6th. There seems to have been a reversal from the era of the 2010s where ASOS sites like Logan often ranked higher than state-wide averages. Now, the warmth is being driven more by coop sites. Blue Hill Observatory in Milton, Mass. notched is 4th hottest July on record. Looks like maybe there's been some amelioration of the urban heat island effect, perhaps by having created a more effective atmospheric blanket over the smaller towns and rural locations, thereby negating the conditions that drove the unbelievable radiational conditions some of these areas used to experience?

This is an interesting map. Number of 90+ days since June 1. All the long-term climate stations along the I-95 are in the top 10, except for NYC, which is tied for 44th. Things that make you go hmmm...

Definitely showing up in the observations with visibility down to 2 1/2 miles.

I would say it is. I asked xAI's Grok to estimate what the climate of New York City would have looked like at the height of the last glacial maximum. I think most here would agree that this is MILES better than the current climate. Month Estimated Mean Temperature (°C) Estimated Mean Temperature (°F) January -15 to -10°C 5 to 14°F February -14 to -9°C 7 to 16°F March -10 to -5°C 14 to 23°F April -3 to 2°C 27 to 36°F May 3 to 8°C 37 to 46°F June 10 to 15°C 50 to 59°F July 12 to 17°C 54 to 63°F August 10 to 15°C 50 to 59°F September 5 to 10°C 41 to 50°F October 0 to 5°C 32 to 41°F November -5 to 0°C 23 to 32°F December -12 to -7°C 10 to 19°F Winter (Dec–Feb): Very cold, with means likely between -15°C and -7°C (5–19°F), similar to modern subarctic or high-latitude tundra climates. Frequent snow was probable, but low precipitation meant less accumulation than in modern snowy regions like upstate New York. Summer (Jun–Aug): Short and cool, with July means likely 12–17°C (54–63°F), resembling modern high-latitude coastal areas (e.g., parts of Iceland or northern Canada). Proximity to the ice sheet and cold Atlantic Ocean currents kept summers chilly. Precipitation and Snow: The climate was drier than today due to cold air holding less moisture. Snow was common in winter, but total accumulation was likely moderate, with a tundra-like landscape. Permafrost was widespread, affecting soil and vegetation. Ice Sheet Influence: The Laurentide Ice Sheet, terminating near Long Island, would have cooled NYC via cold air drainage and albedo effects. Cold ocean currents along the Atlantic coast further suppressed temperatures. Variability: Daily and annual variability was likely high, with cold snaps in winter and occasional warm days in summer. Strong winds from the ice sheet (katabatic winds) could have made conditions feel even colder.

I don't think one night in the upper 30s would do much harm to corn/maize. Obviously, if it was consistently cold (and/or moist) that would affect growth. Consistently warm overnight temperatures are a bigger concern because the plant can respire through the night and burn stored energy faster than it can be replenished. Corn is native to higher latitudes in Mexico. It does best with overnight lows from in the 50s/low 60s.