1 and NCDC uses the entire 20th century.

2 The NCDC has records for thousands of weather stations, some back more than a century.

3 NCDC also reports that the North American snow cover extent for the month was the smallest on record for April.

4 The climate center (NCDC) reports that the Earth's combined land and ocean average surface temperature from January-April was 56 degrees, which is 1.24 degrees above the 20th-century average.

5 South of the mean position of the jet stream, top-ten warmest springs were recorded in Texas, New Mexico, and Louisiana. Image credit: NOAA/NCDC.

6 NCDC in North Carolina is the world's largest archive of weather and climate data.

7 When compared with Figure 2, we see that this is a classic winter La Ni?a pattern, but at extreme amplitude. Image credit: NOAA/NCDC.

8 Both NCDC and NASA use data that goes back to 1880.

9 NCDC also has long-term data-exchange efforts with other countries, including a 20-year program with China.

10 GISS uses a base period of 1951 to 1980; the Met Office uses 1961 to 1990; the Japanese Meteorological Agency uses 1971 to 2000; and NCDC uses the entire 20th century.

11 The data go through rigorous quality-control procedures before they enter the Global Historical Climatology Network, which NCDC uses to monitor long-term trends in temperature and precipitation.