You need to read this study
it goes in depth. But here are the opening paragraphs:
GISS Surface Temperature Analysis
Global Temperature Trends: 2007 Summation
The year 2007 tied for second warmest in the period of instrumental data, behind the record warmth of 2005, in the Goddard Institute for Space Studies (GISS) analysis. 2007 tied 1998, which had leapt a remarkable 0.2°C above the prior record with the help of the "El Niño of the century". The unusual warmth in 2007 is noteworthy because it occurs at a time when solar irradiance is at a minimum and the equatorial Pacific Ocean is in the cool phase of its natural El Niño-La Niña cycle.
Figure 1 shows 2007 temperature anomalies relative to the 1951-1980 base period mean. The global mean temperature anomaly, 0.57°C (about 1°F) warmer than the 1951-1980 mean, continues the strong warming trend of the past thirty years that has been confidently attributed to the effect of increasing human-made greenhouse gases (GHGs) (Hansen et al. 2007). The eight warmest years in the GISS record have all occurred since 1998, and the 14 warmest years in the record have all occurred since 1990.