Climate Change Chart of San Francisco, USA

Overview of climate changes

Temperature changes

Averaged across calendar months, monthly mean temperature shows a difference of +0.87 °C compared with the earlier reference period. This is an unweighted comparison of monthly means, not a day-weighted annual average, and it describes mean temperatures rather than daytime highs. The largest monthly increase was in October, with a difference of +1.38 °C. This identifies the strongest increase among the monthly temperature differences, not a change shared by every month.

Changes in rainfall

Averaged across calendar months, mean daily rainfall had a difference of -0.38 mm/day, indicating lower mean daily amounts in the more recent period. The figure is an unweighted average of calendar-month means, not a day-weighted annual average or a monthly rainfall total. The largest monthly decrease was in February, where mean daily rainfall had a difference of -1.50 mm/day. By contrast, the largest increases were in September / December, with a difference of +0.08 mm/day; these are daily mean amounts, not monthly totals.

Changes in sunshine duration

Across calendar months, mean daily sunshine duration had an average difference of +0.02 hours/day. This is an unweighted comparison of monthly means, so it summarizes the months collectively rather than implying that sunshine increased in every month. The largest monthly increase was in February, with a difference of +0.54 hours/day, while the largest decrease was in July, with a difference of -0.31 hours/day. These contrasting monthly changes show why the small overall mean difference should not be read as a uniform month-by-month shift.

Changes in snowfall

Averaged across calendar months, mean daily snowfall was unchanged at the displayed precision, with a difference of 0.00 mm/day compared with the earlier period. This rounded mean comparison does not establish that snowfall was absent or that every month's value was identical.