There has been significantly more
night-time global warming,
compared with
day-time global warming
since 1975.
We have had "diurnal asymmetry".
Note:
The only significant warming
after the early 2000s,
so far, has been from
the 2015 - 2016 El Nino (ENSO)
heat release, which is
unrelated to man made CO2.
As an example of daytime
vs. nighttime warming,
below are charts
of US average temperatures
for the month of June (1895 to 2018)
where the maximum temperatures,
in the first chart,
show no particular trend,
but June minimum temperatures,
in the second chart,
show significant warming
since 1980:
As an example of daytime
vs. nighttime warming,
below are charts
of US average temperatures
for the month of June (1895 to 2018)
where the maximum temperatures,
in the first chart,
show no particular trend,
but June minimum temperatures,
in the second chart,
show significant warming
since 1980:
Efforts to understand
this night warming effect
has focused on
many variables,
such as cloud cover,
precipitation and
soil moisture content.
The correct explanation,
like a majority of
climate change science,
may be unknown.
The theory that makes
the most sense to me:
I believe boundary-layer depth
is a better explanation
for why night-time temperatures
should be significantly more sensitive
to greenhouse gas warming
than day-time temperatures.
The layer of air
just above the ground
is known as the boundary-layer.
At night this layer is very thin,
just a few hundred meters.
During the day it grows
up to a few kilometers.
In fact, night warming
significantly greater than
day warming is a
greenhouse gas "signature".
It is also a primary reason
for ASSUMING that CO2
is responsible for
the global warming since 1975,
rather than natural climate change,
(that had been the cause
of all climate change
for 4.5 billion years.)
(Another reason to ASSUME
that CO2 is responsible
for global warming since 1975,
is the significant warming
of the Arctic region. ...
But that expected
greenhouse gas "signature"
in the Arctic is contradicted
by the LACK of warming
in Antarctica since 1975,
except for some minor local warming
near underseas volcanoes.)
The build-up of carbon dioxide
in the atmosphere
from human emissions
should reduce the amount
of infrared radiation
released into space as Earth cools.
This should affect (increase)
both the night-time low
and day-time high temperatures.
During the day
sunlight keeps warming
(half) the planet until late afternoon.
CO2 is invisible to sunlight.
Then (half) the planet
starts cooling
until the morning sunrise.
At night there is
a much smaller volume
of boundary layer air
for CO2 to affect
... so there should be
a much larger effect
on the night time low temperature
than on the daytime high temperature,
as measured by surface (land)
weather stations.
In fact, the number of
extremely cold nights
has dropped by half
during the past fifty years.
In addition to warming
measured mainly at night,
the higher average temperatures
in the US since 1975,
have also been mainly
in the winter and spring.
In addition, the hottest decade
in the US was the 1930s,
based on day-time
high temperature records
of the individual states.
I use the US as my example
because we have
the biggest network
of weather stations.
Simulating higher temperatures
at night is one of many problems
with climate models.
Predicting fast warming in Antarctica,
that never happened,
is another climate model problem.
Grossly over predicting
global warming,
by two to three-fold,
is an even bigger
climate model problem.
Climate models
have a lot of problems!