Climate Change Chart of Chicago, USA

Overview of climate changes

Temperature changes

Averaged across calendar months, monthly mean temperature shows a difference of +0.95 °C in the more recent period; this is an unweighted comparison of monthly means, not a day-weighted annual average or a measure of daytime highs. The change was not uniform across the selected monthly extremes: December had the largest increase, a difference of +2.55 °C, while October had the largest decrease, a difference of -0.23 °C. These monthly contrasts describe the reference-period averages for those months, not a continuous trend or conditions in every year.

Changes in snowfall

Mean daily snowfall averaged across calendar months had a difference of -0.09 mm/day in the more recent period; this is an unweighted comparison of monthly means, not a day-weighted annual total. The overall mean difference sits alongside opposing monthly changes: December had the largest decrease, a difference of -1.93 mm/day, while February had the largest increase, a difference of +1.68 mm/day. Thus the period-average comparison masks variation among months; the daily mean amounts should not be read as monthly totals or as a continuous trend.

Changes in sunshine duration

Mean daily sunshine duration averaged across calendar months had a difference of -0.38 hours/day in the more recent period, an unweighted summary of monthly means rather than a day-weighted annual measure. The monthly pattern varied: October recorded the largest decrease, a difference of -1.17 hours/day, while June recorded the largest increase, a difference of +0.40 hours/day. These figures compare reference-period averages and do not describe every day or establish a continuous trend.

Changes in rainfall

Mean daily rainfall, rather than monthly rainfall totals, averaged across calendar months shows a difference of +0.67 mm/day in the more recent period; this unweighted mean summarizes monthly averages and does not imply the same change in each month. Among the largest monthly differences, July had an increase of +2.28 mm/day, whereas November had a decrease of -0.22 mm/day. These are comparisons of daily averages between the two reference periods, not evidence of a continuous change over the intervening years.