The Tapajós National Forest (Flona Tapajós) has been providing important ecosystem services to society since the creation of this Conservation Unit in the Amazon. This study analyzed two climatic series from Belterra to identify possible effects on the thermal regime in the municipality as a function of the proximity of the Flona Tapajós and the consolidated grain production center in western Pará. Two climatological normal datasets from the National Institute of Meteorology (INMET) were analyzed (1961-1990 and 1981-2010). Analysis of variance was used to compare averages, extremes (minimums and maximums), and thermal amplitudes. Average temperature was 24.6 °C in the first semester (1961-1990) and 25.2 °C (1981-2010), with maximums of 29.4 °C and 29.9 °C, and minimums of 20.6 and 21.2 °C, respectively. There were no statistical differences in these comparisons. In the second semester the averages increased to 25.2 °C and 26.0 °C, and were statistically different, with maximums of 31.2 °C and 31.6 °C and minimums of 20.4 °C and 21.2 °C, indicating different thermal regimes during 1981-2010. Additionally, from October to December the nights were warmer. The Flona Tapajós may have experienced a reduction in provision of ecosystem services, and the increase in minimum temperatures could be associated with grain production activities in the region.