The Nighttime Heat Jerk Has Entered a New Regime
The contiguous United States has just experienced its hottest meteorological summer on record. The 2026 summer provides an extraordinary example of the nighttime component of climate energy—a summer average minimum temperature of 61.71°F—the highest recorded between 1895–2026.
A change this pronounced over such a short period is precisely why looking exclusively at long-term linear warming can obscure emerging nonlinear behavior. The important observation here is the change in the rate of change. Over the last six years, that change has become extreme.
The contiguous United States has just experienced its hottest meteorological summer on record—and one of the most revealing characteristics of the 2026 climate signal is not simply how hot the afternoons became, but how much heat remained after the sun went down.
The National Oceanic and Atmospheric Administration (NOAA) reports that the average temperature across the lower 48 states during June–August 2026 reached 74.4°F, 3.0°F above the 20th-century average. That surpassed the previous summer records set in 1936 and 2021 by 0.4°F.
But averages can conceal the behavior of a nonlinear climate system. To understand what is happening, it is useful to examine nighttime minimum temperatures separately from daytime maximum temperatures.
Nighttime temperatures are becoming an increasingly important component of the climate system because nighttime is normally a period of thermal recovery. After sunset, the land surface, buildings, pavement, vegetation, soils and water bodies can release some of the energy accumulated during the day.
When nighttime temperatures remain unusually high, that recovery period becomes less effective. The next day begins with a warmer baseline, meaning that the system has less opportunity to dissipate the heat accumulated during the previous day.
A hot afternoon followed by a cool night is therefore one type of heat event. A hot afternoon followed by an unusually warm night, followed by another hot afternoon, is something different: the heat becomes cumulative.
The 2026 summer provides an extraordinary example of this nighttime component of climate energy. The NOAA CONUS June–August minimum-temperature dataset shows a summer average minimum temperature of 61.71°F in 2026, the highest value in the supplied 1895–2026 series.
The historical data show that nighttime minimum temperatures have not simply risen in a smooth, linear fashion.
For this analysis, the NOAA CONUS June–August minimum-temperature series was divided into three periods: 1990–2010, 2010–2020 and 2020–2026. The purpose is to examine not only temperature change, but the changing rate of temperature change.
The NOAA dataset identifies itself as “Contiguous U.S. June-August Minimum Temperature” and reports the observations in degrees Fahrenheit. The actual summer values show the transition particularly clearly. The 1990 summer Tmin was 59.19°F, while 2010 reached 60.68°F. The 2020 value was 60.64°F, followed by 61.71°F in 2026.
Thus, the nighttime signal did not simply march upward at a constant rate. It slowed during one period and then accelerated sharply during the most recent period.
1990–2010: The Initial Warming Regime
Between 1990 and 2010, the CONUS summer minimum-temperature trend was approximately +0.5774°F per decade.
The actual endpoints were 59.19°F in 1990 and 60.68°F in 2010, while the linear regression across all observations in the interval produces the +0.5774°F/decade trend velocity.
This establishes the first baseline velocity:
V₁ = +0.5774°F/decade
This is warming, but by itself it does not establish acceleration or jerk. It simply tells us how rapidly summer nighttime minimum temperatures were changing during this period.
2010–2020: A Temporary Deceleration
Between 2010 and 2020, the linear trend in CONUS summer Tmin was approximately −0.0345°F per decade. The endpoint values were 60.68°F in 2010 and 60.64°F in 2020.
Thus:
V₂ = −0.0345°F/decade
The 2010–2020 interval represents a slight deceleration—or temporary reversal—in the long-term summer nighttime warming trajectory. That is important because it prevents the analysis from becoming a simple story of uninterrupted acceleration. The climate signal contains variability. A nonlinear system can experience periods of slower change followed by periods of rapid acceleration.
The important question is what happened next.
2020–2026: The Acceleration Returns
The answer is visible in the 2020–2026 data. The 2020 summer minimum temperature was 60.64°F. It then rose to 61.45°F in 2021, 61.21°F in 2022, 60.26°F in 2023, 61.09°F in 2024, 60.87°F in 2025 and 61.71°F in 2026.
The individual years fluctuate, but the linear trend over the seven observations is approximately:
V₃ = +0.6893°F/decade
That is a remarkable reversal from the −0.0345°F/decade trend of 2010–2020.
The 2020–2026 warming velocity is also approximately 19% greater than the +0.5774°F/decade velocity calculated for 1990–2010.
The Nighttime Temperature Jerk
This is where the Climate Jerk framework becomes useful.
A temperature trend describes the first derivative:
V = dT/dt
Acceleration describes the second derivative:
A = d²T/dt²
Jerk describes the third derivative:
J = d³T/dt³
The important question therefore changes from “Are nighttime temperatures getting warmer?” to “Is the rate at which nighttime temperatures are changing itself changing?”
Using the three regression-derived velocities, the transition from 1990–2010 to 2010–2020 produces an acceleration of approximately:
A₁ = −0.4080°F/decade²
The transition from 2010–2020 to 2020–2026 produces:
A₂ = +0.9048°F/decade²
The acceleration therefore changes from negative to strongly positive.
Using the midpoint of each trend interval and calculating the rate of change between those acceleration regimes produces a finite-difference nighttime-temperature jerk of approximately:
J = +1.14°F/decade³
Nighttime Temperature Jerk ≈ +1.14°F/decade³
What the Number Means
The +1.14°F/decade³ value should not be interpreted as though the temperature itself suddenly increased by 1.14°F. It is a third-order rate-of-change measurement.
The first number tells us the temperature is changing. The second tells us whether that temperature change is accelerating or decelerating. The third tells us whether that acceleration is itself changing.
In this analysis, the progression is:
+0.5774°F/decade → −0.0345°F/decade → +0.6893°F/decade
The corresponding acceleration changes from:
−0.4080°F/decade² → +0.9048°F/decade²
That produces:
+1.14°F/decade³ jerk
The significance is therefore not that every year must be warmer than the preceding year. The significance is that the underlying rate of nighttime warming underwent a substantial reversal and acceleration during the 2020–2026 interval. This is consistent with the concept of nonlinear acceleration: the climate system does not have to follow a smooth upward curve for its rate of change to become increasingly consequential.
The 2026 value of 61.71°F is particularly important because it represents the highest June–August CONUS minimum-temperature value in the supplied 1895–2026 dataset. That record arrives after a period in which the nighttime warming velocity had temporarily weakened.
The sequence is therefore more revealing than any single year’s temperature:
1990–2010: +0.5774°F/decade
2010–2020: −0.0345°F/decade
2020–2026: +0.6893°F/decade
The system went from substantial warming, to a period of near-zero change, to substantially faster warming. That is the behavior we are calling nighttime-temperature jerk.
Nighttime temperatures also change the physical meaning of extreme heat. Consider two hypothetical summer days that both reach 100°F. In the first case, the temperature falls to 65°F overnight. In the second, it falls only to 80°F.
The daytime maximum is identical. The thermal burden is not. In the second scenario, the environment begins the next day 15°F warmer. If that pattern persists for several consecutive days, the system has progressively less opportunity to release accumulated heat.
A heatwave should therefore not be viewed solely as a sequence of daytime maximum temperatures. The overnight minimum matters because it determines how much recovery occurs before the next cycle begins. A warming night effectively raises the starting line for the following day.
The nighttime signal is also part of a broader hydroclimatic system involving evaporation, soil moisture and drought. The relentless combination of heat and limited moisture can cause drought to expand rapidly. By September 1, drought conditions covered 59.1% of the contiguous United States.
Heat increases atmospheric demand for moisture. That accelerates evaporation from soils, vegetation, reservoirs and surface water. As soils dry, evaporative cooling can decline, leaving more energy available to heat the land surface.
The feedback becomes:
Heat → evaporation → drying → drought → reduced evaporative cooling → more heat.
The result is not simply a hotter landscape. It is a landscape increasingly vulnerable to additional heat.
Nighttime warming adds another component to this process. If the land does not cool sufficiently overnight, the following day begins with elevated thermal energy already present in the system. That can increase heat stress, reduce nighttime recovery and contribute to cumulative thermal loading.
The sequence becomes:
Daytime heat → nighttime heat retention → reduced recovery → warmer starting conditions → greater next-day heat → additional energy accumulation.
This is why nighttime minimum temperatures may be especially useful for detecting changes in the behavior of the climate system. They tell us something about what happens to accumulated energy after the sun disappears.
The Three-Period Signal
The three-period analysis can be summarized numerically:
| Period | Summer Tmin Trend | Warming Velocity | Change in Velocity |
|---|---|---|---|
| 1990–2010 | +0.5774°F/decade | +0.5774°F/decade | — |
| 2010–2020 | −0.0345°F/decade | −0.0345°F/decade | −0.6119°F/decade |
| 2020–2026 | +0.6893°F/decade | +0.6893°F/decade | +0.7238°F/decade |
The corresponding accelerations are:
1990–2010 → 2010–2020: −0.4080°F/decade²
2010–2020 → 2020–2026: +0.9048°F/decade²
And the resulting finite-difference jerk is approximately:
+1.14°F/decade³
This is not a claim that the climate system follows a perfect mathematical curve. It is a measurement of how dramatically the estimated nighttime warming rate changed between the three selected periods.
For generations, the heat of summer was primarily experienced as something that happened during the day. That distinction is becoming increasingly inadequate. The afternoon heat is only one part of the energy balance. The nighttime minimum determines how much of that accumulated energy is released before the next day’s solar heating begins.
When nighttime temperatures remain elevated, the recovery period contracts. When recovery contracts, heat accumulates. When heat accumulates, the next extreme event starts from a higher baseline. And when the rate of nighttime warming itself changes rapidly, the system begins exhibiting the type of nonlinear behavior described by the Climate Jerk hypothesis.
The phrase “hot summer nights” sounds almost harmless.
It isn’t.
A warmer night means less recovery. Less recovery means greater cumulative heat exposure. Greater cumulative heat exposure increases stress on people, ecosystems, water supplies and infrastructure. The 2026 NOAA data provide a particularly striking endpoint to this story: a CONUS June–August minimum-temperature average of 61.71°F, the highest value in the supplied historical series.
More importantly, the trend analysis shows a dramatic change in the rate of nighttime warming. The velocity increased from −0.0345°F/decade during 2010–2020 to +0.6893°F/decade during 2020–2026.
That change corresponds to an estimated acceleration of +0.9048°F/decade² during the most recent transition and an overall finite-difference jerk of approximately +1.14°F/decade³.
So the question is no longer simply:
How hot is it getting?
The more consequential question is:
How quickly is the system changing how quickly it gets hotter?
That is where the jerk matters. Climate energy is not merely raising the temperature. It may be changing the rate at which the temperature changes. And increasingly, the evidence is showing up after the sun goes down.
The most important finding in the nighttime-temperature record is not simply that summer nights are getting warmer. It is that the rate of nighttime warming has changed dramatically during the past six years.
The 2020–2026 interval marks a striking departure from the relatively weak nighttime-temperature change observed during 2010–2020. In the NOAA CONUS June–August Tmin series, the estimated warming velocity shifts from approximately −0.0345°F per decade during 2010–2020 to +0.6893°F per decade during 2020–2026. That is a reversal of direction and an enormous change in the rate of temperature change.
NOAA’s independent 2026 observations reinforce the signal: July’s CONUS average nighttime minimum reached 64.2°F, 3.7°F above the 20th-century average, the warmest monthly average minimum temperature in the record.
This is where the concept of Climate Jerk becomes particularly useful. Temperature is the first-order signal; warming velocity is the first derivative; acceleration is the second derivative; and jerk is the third derivative—the rate at which acceleration changes.
Using the three-period analysis, nighttime-temperature acceleration shifts from approximately −0.4080°F/decade² in the 1990–2010 → 2010–2020 transition to +0.9048°F/decade² in the 2010–2020 → 2020–2026 transition. The resulting finite-difference estimate of nighttime-temperature jerk is approximately +1.14°F/decade³.
The significance of that number is not that temperatures suddenly increased by 1.14°F. They did not. The number describes the changing behavior of the warming rate itself. During 2010–2020, the summer nighttime trend was essentially flat. During 2020–2026, the trend became strongly positive. The system therefore moved from deceleration into substantial acceleration within a remarkably short interval.
The six-year window is especially important because it represents only a fraction of a conventional climate trend period. A change this pronounced over such a short period is precisely why looking exclusively at long-term linear warming can obscure emerging nonlinear behavior. A long-term average can tell us where the climate has been heading; it can be much less informative about how rapidly the trajectory is changing now.
And the 2026 record did not occur in isolation. NOAA reports that much-above-average nighttime minimum temperatures covered most of the contiguous United States during summer 2026, while record nighttime warmth occurred across California, Nevada, Arizona, Utah, New Mexico and Colorado in August. At the same time, the CONUS experienced its hottest meteorological summer on record, with an average temperature of 74.4°F—3.0°F above the 20th-century average.
That combination matters because nighttime heat is effectively a form of thermal memory. A cooler night allows the land and built environment to discharge some accumulated energy. A warmer night leaves more energy in the system when the next day begins. As nighttime temperatures rise, the recovery interval becomes less effective, and consecutive hot days can become increasingly connected rather than functioning as independent events.
The 2020–2026 period therefore represents more than another step upward on a temperature graph. It represents a compression of the nighttime recovery cycle. The climate system is increasingly carrying heat from one day into the next.
That has consequences beyond human discomfort. Persistent nighttime warmth can increase cumulative heat stress, extend cooling demand, reduce ecological recovery and interact with soil-moisture and drought feedbacks. NOAA reported that drought covered 59.1% of the CONUS by September 1, 2026, an increase of more than 10 percentage points from early August.
The broader feedback can be expressed simply:
Heat → evaporation → drying → drought → reduced evaporative cooling → more heat.
Nighttime heat adds another component:
Daytime heat → nighttime heat retention → reduced recovery → higher starting temperature → greater next-day heat → additional heat retention.
This is why the nighttime signal deserves to be treated as an Earth-system variable rather than merely a measure of sleeping comfort.
The evidence does not show a perfectly smooth acceleration. In fact, the 2010–2020 slowdown makes the subsequent acceleration more—not less—interesting. Nonlinear systems do not necessarily accelerate continuously. They can pause, fluctuate, reorganize and then rapidly shift into a new regime. The important observation here is the change in the rate of change.
Over the last six years, that change has become extreme.
The nighttime warming velocity went from approximately −0.0345°F/decade to +0.6893°F/decade. The associated acceleration jumped to approximately +0.9048°F/decade², producing a calculated finite-difference nighttime-temperature jerk of approximately +1.14°F/decade³.
That is the number to watch:
+1.14°F/decade³
It does not mean that every subsequent year will necessarily be warmer than the previous year. It means that, across the selected intervals, the rate at which summer nighttime temperatures are changing has undergone a powerful positive reversal.
And that may be the most important lesson from the hottest summer ever recorded in the contiguous United States.
The climate system is not merely getting hotter.
It is changing how quickly it gets hotter—and increasingly, that change is happening at night.
Nighttime Reading
Tonight’s homework assignment is my favorite: Deep, deep math, statistics, and climate physics.
THE NIGHTTIME HEAT JERK HAS ENTERED A NEW REGIME
The contiguous United States just experienced its hottest meteorological summer on record. But the really interesting signal may be happening after sunset. Summer 2026 averaged 61.71°F for daily minimum temperatures—the warmest summer nighttime average ever recorded.
Nighttime is normally the atmosphere’s recovery period. After sunset, land, pavement, buildings, vegetation, soils, and water can release some of the energy accumulated during the day. But what happens when the recovery period itself starts getting hotter?
That’s where Climate Jerk comes in.
Temperature = the signal.
Warming rate = the first derivative.
Acceleration = the second derivative.
Jerk = the third derivative—the rate at which acceleration changes.
Using a three-period analysis, nighttime-temperature acceleration shifted from approximately −0.4080°F/decade² during the 1990–2010 → 2010–2020 transition to +0.9048°F/decade² during the 2010–2020 → 2020–2026 transition.
That produces an estimated nighttime-temperature jerk of approximately:
+1.14°F/decade³
That does NOT mean temperatures suddenly increased by 1.14°F. It means the behavior of the warming rate changed dramatically. From 2010–2020, the summer nighttime trend was essentially flat. From 2020–2026, it became strongly positive.
The climate system moved from deceleration into substantial acceleration in only six years.
And that matters. The six-year window is especially important because it represents only a fraction of a conventional climate trend period. A change this pronounced over such a short period is precisely why looking exclusively at long-term linear warming can obscure emerging nonlinear behavior. A long-term linear trend tells us where the climate has been going. It may not tell us how rapidly the trajectory is changing right now.
The 2026 nighttime record did not occur in isolation. Much-above-average nighttime minimum temperatures covered most of the contiguous United States, while record nighttime warmth occurred across much of the Southwest.
Meanwhile, the CONUS recorded its hottest meteorological summer ever: 74.4°F, or 3.0°F above the 20th-century average. Think of nighttime heat as thermal memory. A cooler night allows the system to discharge some accumulated energy. A warmer night leaves more energy behind when the next day begins. That can make consecutive hot days increasingly connected rather than independent events.
The most important observation isn’t simply that nights are getting warmer.
It is that the RATE OF CHANGE OF THE RATE OF CHANGE has changed.
And over the last six years, that change has become extreme.
Homework assignment: Do the math.
Then ask yourself what happens when a nonlinear climate system stops merely warming—and starts changing how quickly it warms.
