If someone asked you to (56) _____out if the Earth’s climate had changed over the past century, your first instinct would be reach for the meteorological records, just as climate change researchers have done (57) for decades. But boreholes - holes drilled in the ground in (58) ____ of resources such as oil and water - might give you a better answer. Over the past fifty years, mineral, oil and gas exploration companies have drilled thousands of boreholes all (59) _____the world. In some cases, geophysicists have drilled boreholes to study (60) ____temperature varies with depth in the upper sections of the Earth’s crust. Now climatologists are recognizing that these measurements, many of (61) _____were discarded as unimportant by the geophysicists, offer power clues to the Earth’s past (62)_____, possibly, future climate. Already, analyses of temperature readings from boreholes are producing provocative findings. They suggest that at (63) ____ part of the global warming (also known as the (64) ____ seen in the meteorological records of the past century can be explained (65) ____ natural fluctuations in the Earth’s underground temperature.