world experience average temperatures of 56.4 °f -lrb- 13.6 °c -rrb- last month - 1.5 °f above average for the 20th century .
first 3 months of 2015 have set new high temperature marks , and the trend could continue throughout the year .
scientists warn fossil fuels are pushing greenhouse gas into the atmosphere , leading to increased temperatures .
but el niño , a blob of record hot water in the northeast pacific ocean , could also be driving up temperatures .