Climate Change Chart of Philadelphia, USA

Overview of climate changes

Temperature changes

Averaged across calendar months, the difference in monthly mean temperature was +0.72 °C compared with the earlier reference period; this unweighted summary describes the monthly means collectively, not a day-weighted annual average or daytime maximum temperatures. The largest monthly increase was in December, with a difference of +2.21 °C. By contrast, November recorded the largest monthly decrease, a difference of -0.38 °C. These opposing monthly differences show that the aggregate mean does not describe every month’s direction.

Changes in rainfall

Mean daily rainfall, rather than monthly rainfall totals, had an unweighted difference across calendar-month means of +0.30 mm/day. The largest monthly increase occurred in October, where the difference was +1.36 mm/day; this identifies a change in that month’s daily mean, not a total accumulated over the month. In November, the largest monthly decrease was a difference of -0.48 mm/day. The aggregate increase therefore should not be read as a rise in every month.

Changes in snowfall

Mean daily snowfall showed an unweighted difference across calendar-month means of +0.33 mm/day. The largest monthly increase was in March, with a difference of +2.28 mm/day, while December had the largest monthly decrease, a difference of -0.47 mm/day. These figures describe mean daily amounts, not monthly snowfall totals, and the aggregate difference does not mean every month changed in the same direction.

Changes in sunshine duration

Averaged across calendar months, mean daily sunshine duration had a difference of -0.18 hours/day. Monthly shifts went in both directions: July had the largest increase, at a difference of +0.85 hours/day, while February had the largest decrease, at a difference of -0.80 hours/day. These are differences in mean daily hours, and the overall average across calendar-month means does not imply that sunshine duration moved the same way in every month.