Since late 1992, instruments on satellites have been collecting data that scientists use to calculate the average global sea level. Averaging the 8 available datasets, it increased by 2.0 inches (50 mm) between the 1990s and the recent decade from 2011 to 2020. Some have claimed that sea level is rising at an accelerating rate, but the fact is that global sea-level accelerations are so close to zero that they can be positive, zero, or negative depending upon the timeframe that scientists analyze. Thus, a 2011 paper in the Journal of Coastal Research reviewed the results of numerous sea-level acceleration studies and concluded that there is "disagreement" over whether acceleration can "be detected." Local tide gauges indicate that sea levels have been generally rising since 1860 or earlier. This is about 45 years before surface temperatures began to rise and 75 years before man-made emissions of CO2 reached 1% of natural emissions.