This temperature update presents the NASA satellite measurements of monthly temperature anomalies—the difference between the observed values and the 1979–1998 mean values. Global satellite measurements are made from a series of orbiting platforms that sense the average temperature in various atmospheric layers. Here, we present the lowest level, which matches nearly perfectly with the mean temperatures measured by weather balloons in the layer between 5,000 and 28,000 feet. The satellite measurements are considered accurate to within 0.01°C and provide more uniform coverage of the entire globe than surface measurements, which tend to concentrate over land.
April 2003: The global average temperature departure was 0.14°C; the Northern Hemisphere temperature departure was 0.25°C; and the Southern Hemisphere departure was 0.03°C.
Below: Monthly satellite temperatures for the Northern Hemisphere (top) and Southern Hemisphere (bottom). Trend lines indicate statistically significant changes only.
From the graphs that you posted, it appears that the Northern Hemisphere has warmed up 0.3 - 0.4 deg C (0.5 - 0.7 deg F) during the past 24 years, while the Southern Hemisphere has stayed constant.
What do you think is the cause?