Studies indicating historical CO2 levels lag behind temperature have merit, confirms Peter Hildebrand, Director of Earth Science at NASA's Goddard Space Flight Center. Responding to a question on

Studies indicating historical CO2 levels lag behind temperature have merit, confirms Peter Hildebrand, Director of Earth Science at NASA's Goddard Space Flight Center. Responding to a question on Twitter, Hildebrand explained that in the pre-industrial age, temperature changes drove CO2 levels; a warmer climate caused the biosphere to emit more CO2.

However, in the post-industrial era, this dynamic has reversed. Now, increasing atmospheric CO2 is leading to higher temperatures, indicating a fundamental shift in the physical-biological processes. For more information, visit Ask A Climate Scientist.

JPL scientist Josh Willis, from NASA's Ask A Climate Scientist campaign, asserts that global warming is not pausing, despite some decades showing slower surface temperature

JPL scientist Josh Willis, from NASA's Ask A Climate Scientist campaign, asserts that global warming is not pausing, despite some decades showing slower surface temperature increases.

Willis points to increased ocean heat trapping and continuously rising sea levels as clear evidence. See [global temperature trends](http://climate.nasa.gov/key_indicators#globalTemp) and [sea level records](http://climate.nasa.gov/key_indicators#seaLevel).

While natural fluctuations occur, human-caused climate change is undeniably progressing. Explore more NASA climate science answers [here](http://bit.ly/1b7rSdL).

This video explains the Hydrologic Cycle, also known as the Water Cycle, through animation, graphics, and video clips. It illustrates key "flow" and "storage" processes, including precipitation,

This video explains the Hydrologic Cycle, also known as the Water Cycle, through animation, graphics, and video clips. It illustrates key "flow" and "storage" processes, including precipitation, interception, runoff, infiltration, percolation, groundwater discharge, evaporation, transpiration, evapotranspiration, and condensation.

Published on July 12, 2013.

Physicist Lee Smolin compares the scientific community's function to democracy. He explains that scientists "fight

Physicist Lee Smolin compares the scientific community's function to democracy. He explains that scientists "fight and argue as hard as we can," yet accept that the next generation will ultimately decide what is correct.

Smolin argues this process mirrors how democracy operates. More of his lectures are available on his website.

Leroy Little Bear delivered the Spring 2011 Simon Ortiz and Labriola Center Lecture on Indigenous Land, Culture and Community. Recorded March 24, 2011, at the Heard Museum in Phoenix, Arizona (