Climate Change Chart of Jamestown, Saint Helena, Ascension and Tristan da Cunha

Overview of climate changes

Temperature changes

Averaged across calendar months, monthly mean temperature shows a difference of +0.11 °C. This is an unweighted mean of the monthly averages, not a day-weighted annual average, and it does not imply that every month warmed. The largest monthly increase was in May, with a difference of +0.26 °C; the largest monthly decrease was in October, with a difference of -0.12 °C. These are changes in monthly mean temperature, not daytime maximum temperatures, and describe the most pronounced monthly shifts rather than a continuous trend.

Changes in rainfall

Mean daily rainfall, averaged across calendar months, had a difference of +0.15 mm/day. This unweighted comparison of monthly means is not a day-weighted annual average, and the mean difference should not be read as a change occurring in every month. The largest monthly increase was in December, with a difference of +0.36 mm/day, while the largest monthly decrease was in June, with a difference of -0.03 mm/day. These figures describe mean daily amounts for the named months, not monthly rainfall totals; they identify the most pronounced monthly differences without establishing a continuous pattern.

Changes in sunshine duration

Mean daily sunshine duration, averaged across calendar months, had a difference of -0.29 hours/day. This is an unweighted average of the monthly means rather than a day-weighted annual average, so it summarizes the calendar-month comparison without implying the same change in each month. The largest monthly decrease was in August, with a difference of -0.72 hours/day in mean daily sunshine duration. It marks the strongest monthly reduction in the supplied comparison, not a continuous trend or a description of every day in that month.