A seemingly
cold and wet weather in July this year has prompted some brain-devoid denialist
to call into question an only accelerating global warming. In fact the previous
month was not cooler nor wetter than 1991-2020 average. Mean temperature in
July 2025 reached +19.9C, vs. long-term average of +19.7C and total precipitation
reached 54.4 millimetres, vs. long-term average of 82.2 millimetres.
Although
there is little chance I convince conspiracy theorists, I resolved to take
little autistic delight in playing with numbers and compiling chart showing how
the climate in the capital of Poland has evolved since 1951. In my analysis I
fully rely on resumed and revamped Meteomodel page, which in turn has
brilliantly processed raw data available from the Polish Met Office (IMGW).
First comes
a standard temperature by month chart, with three lines representing 30-year
averages in three measurement periods. They illustrate climate change dynamics
in the perspective of two decades. You can clearly see winters and summers are
"most affected" periods, while in spring and autumn average
temperature increase at a slower pace.
From this
chart on, I begin to illustrate long-term trends with rolling 10-year and
30-year averages. The outcomes clearly indicate mean yearly temperature in
Warsaw has risen by more than 1 Celsius degree over the last 40 years and the
warming has speeded up over the last decade.
Looking at
winter months only (note 0 on the horizontal axis stands for 0C), we see harsh
winters are the thing of the past, the last such one was in 2012/13. The recent
winters with mean temperatures above 0C do not even meet the formal definition
of a winter.
For summer
months, the temperature incline trend is even clearer. Today one forgets
summers with average temperature below +17C were quite prevalent in 1960s and
1970s. Note the 10Y rolling average has gone up by 3 Celsius degrees over
merely four decades.
One of the
biggest reasons to worry about the impact of the climate change are heat waves.
The number of days defined as hot back in the second half of the twentieth
century ran at 5 a year on average. In recent two decades it skyrocketed. Hence
summer 2025 with 4 hot days so far is perceived as mild.
But quite
often temperatures only nears +30C and this is captured by the chart showing
number of days with day-time high above +25C. Here the trend is also clear,
however less disturbing.
Heat waves
are periods of misery not because of hot afternoons, but due to nights which do
not bring relief. A few decades ago heat was more bearable than these days, as dawns
with minimum temperature above +20C were an absolute rarity. The stats however,
do not capture several nights with temperature dropping for a few minutes
barely below +20C. Counting them would require lots of manual work, which at
the moment is none of my priorities.
The number
of days with frost declines, yet here the tendency is much slower than for
warmth-related figures. A few decades ago a frost in May was quite usual. These
days ground frosts in May happen, but two metres above ground temperature stays
positive. Half of 10 recent Octobers were frost-free, while there has been no
frost-free April so far (the earliest last frost reported on 2 April 2016.
The number
of days with no thaw in turn decreased more dramatically, especially in recent
years, heralding a demise of proper winters. Winters in Warsaw may soon have a
through-zero pattern, with snow or sleet falling and melting and slippery
surfaces being a plague.
A few
decades ago Warsaw saw around 20 days with double-digit frost in mornings.
Looking at the last decade such number dropped close to 5, with some winters
with all-season lows above -10C. And within last 13 years temperature dropped
below -20C only once, on 18 January 2021. Before 1990 such harsh frosts were
observed every second or third year.
If winter,
then snow. Here numbers bring even more ample evidence of winters retreating.
The 10Y average number of days with snow cover peaked in 1971 close to 80,
while in 2025 it fell to little more than 30. Here of note are mild winters
from late 1980s and early 1990s which for a while gave way to proper winters,
the last proper one ending in April 2013. It was all downhill since then.
Hope you've
enjoyed the read to the same extent to which I've drawn pleasure from compiling
this bunch of charts and accompanying comments.
Not a
posting next week (off to Góry Świętokrzyskie).
