In his April 22 letter to the editor, David Powell suggests that the last Ice Age was millions of years ago and due to natural processes.

He is correct that ice ages and the associated interglacial periods are the result of natural causes. The causes are called Milankovitch cycles that are governed by the oblique orbit of earth around the sun plus the 23 degree tilt of the earth on the axis.

Although the duration of the cycles remains a matter of analysis — estimated to be approximately 100,000 years — it is clear that no human impact has historically driven the cycles. The last Ice Age ended approximately 11,700 years ago. At its peak, there was nearly a mile of ice over Whidbey Island. During this glacial period, there was sufficient water tied up in continental ice to drop sea levels by approximately 370 feet. Current Alaska and Siberia were joined by a broad corridor referred to as Beringia more than 600 miles wide.

It was across Beringia that the first humans travelled to reach North America. Human artifacts and/or remains dated to around 24,000 years ago have been found along with human habitation until rising sea levels from the glacial melt around 11,000 years ago submerged the land corridor. The current climate change is unrelated to a Milankovitch cycle. The “greenhouse effect” is well documented by science and is driven by anthropogenic modification of the atmosphere. Carbon dioxide levels have increased from 280 parts per million to over 400 ppm since the beginning of the industrial revolution.

Antarctic glacial ice records of trapped atmospheric gasses show this to be the highest carbon dioxide level in the past 800,000 years. Methane levels have more than doubled with corresponding increases in other human-generated gases, including nitrous oxide, ozone, and fluorocarbons. The annual carbon dioxide emission rate, primarily from burning fossil fuels, in 2015 was nearly 40 gigatons and rising. A gigaton is a million tons! The current rapid — and measurable — melt of both the West Antarctic Ice Sheet and Greenland’s ice cap, along with melting montane glaciers, are projected to increase sea levels globally by as much as six feet by the end of this century. Rising ocean temperatures and increasing levels of ocean acidity — carbon dioxide absorbed as carbonic acid — are currently having devastating effects on ocean ecosystems.

I strongly recommend that Mr. Powell and others who do not believe that climate change is real and primarily caused by humans take the time to actually look at the data coming from science. We have been given the task of stewardship of this marvelous creation. It is time that we take that role seriously. I encourage all readers to participate in the Climate March scheduled for 10 a.m. Saturday, April 29 starting at Whidbey Island Center for the Arts in Langley.

Joe Sheldon is a Coupeville resident and founding board member of the Pacific Rim Institute for Environmental Stewardship. He is a college professor and holds a Ph.D in environmental science.