Sen. John Kerry, D-Mass., and his wife, Teresa Heinz Kerry, have sent out an email to supporters inviting them to a book signing Saturday, April 21 at noon at the First Parish Church in Cambridge, Mass., to discuss their recently released book This Moment on Earth and signing copies. Tickets for the event are $5, which can be put toward the purchase of the book.

"The environment, and the movement that grew up to protect it, is under attack -- concerted and purposeful," the couple said in their email. "Yet the need for solutions to pressing environmental problems grows more urgent each day. A myriad of environmental problems are occurring in the world today, from contamination of the air and water supply to human-induced global climate change."

"This book grows out of a long-held passion we've both had about this movement. Throughout the last three decades, we have both dedicated ourselves to improving our environment -- from national efforts like protecting the Arctic National Wildlife Refuge from being opened to oil and gas drilling, to efforts focused on our home state like securing federal funds to keep Massachusetts at the forefront of climate-friendly technologies," the email adds.

Proceeds from the sales of This Moment on Earth go to The Silent Spring Institute, Save the Harbor/Save the Bay, and Second Nature.

Tickets are on sale from Harvard Book Store now, and will be available at the door.