Global Climate Report - September 2019
Mean Monthly Temperature Records Across the Globe

« Global Climate Report - September 2019


Mean Monthly Temperature Records Across the Globe

Overview

Beginning with the September 2019 Global Climate Report, NOAA is releasing the mean monthly temperature records product. This product provides historical perspectives on the occurrences of warm or cold mean monthly temperatures across the globe from the gridded (5° by 5°) NOAAGlobalTemp. On a monthly basis, the percentage area of the globe experiencing record warm or record cold conditions is reported as a time series for the month from 1951 to the present, complementing the percentile maps. In addition, the ratio of warm-to-cold records is plotted as a time series. For example, a ratio value of 2 indicates that the global area experiencing record warm mean monthly temperatures over the most recent month was 2 times larger than the global area experiencing record cold conditions. Time series of these ratios computed from seasonal (December–February, March–May, June–September, September–November) or annual (January–December) aggregations of monthly mean temperature records will also be produced.

Methodology

Only grid cells that are completely free of missing values from 1951-present are utilized in the analysis, generally limiting our domain to 45°S to 75°N. For each retained grid cell, the warmest and coldest mean monthly temperatures in the 1951-present period of record are identified for each month. These monthly records are expressed as percent areas aggregated over 3 spatial domains: global land-only areas, global ocean-only areas, and the combined global land and ocean. The spatial aggregation accounts for differences in grid cell size with latitude (i.e., cosine weighting) as well as the fraction of land and ocean areas within coastal grid cells. Monthly ratios are computed by dividing the areal extents experiencing warm records with the areal extents experiencing cold records. For seasonal and annual aggregations, the warm and cold record areal extents are summed separately before dividing the totals.

  • Ratio values between 0.8 (five-to-four) and 1.25 (four-to-five) are shown in gray.
  • Red circles indicate values above 1.25.
  • Blue circles indicate values below 0.8.
  • Dark red (dark blue) values represent one of two things:
    • A ratio value that is greater than 50 (less than 0.02)
    • An observation in which the warm (cold) record area is non-zero and the cold (warm) record area is zero.
  • In rare cases, the warm and cold record areas are both zero, in which case the value would be shown as a dark gray circle over unity (i.e., a value of 1).

September 2019 Global Land and Ocean

During September 2019, 7.93% of the world's land and ocean surfaces had a record warm September; however, no land or ocean areas had a record cold September temperature. This was the second highest percentage for record warm temperatures across the globe since 1951, trailing behind September 2015 (14.97%). September 2019 marked the 23rd consecutive year in which less than 1% of the globe had record cold September temperatures. Compared to all months, September 2019 had its 24th highest percentage of the globe with record warm temperatures in the 825-monthly record. October 2015 had the largest percentage at 21.72% of the globe with record warm temperatures. There have been more warm record areas than cold record areas since September 1997.

Record warm September temperatures across the global land encompassed 10.49% of the global land surface—the second highest on record, behind September 2015 (13.85%). However, no land area had a record cold September temperature during September 2019.

About 6.59% of the global ocean surfaces had a record warm September during September 2019. This was the third highest percentage for record warm Septebmer ocean temperatures in teh 69-year record. Only Septembers of 2015 (15.48%) and 2010 (7.90%) had a higher percentage. No ocean area had record cold September temperatures.


Citing This Report

NOAA National Centers for Environmental Information, State of the Climate: Global Climate Report for September 2019, published online October 2019, retrieved on November 21, 2019 from https://www.ncdc.noaa.gov/sotc/global/201909/supplemental/page-4.

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