Make Room! Make Room!
by Harry Harrison (1966)

An effective take on the overpopulation theme, with a surprise ending which horrifies with its casual morbidity. Near-future (1999) NYC is riddled with crime and violence, while culinary delights are practically a thing of the past. A cop rooming with a man old enough to remember real food investigates a murder. Filmed as Soylent Green.

Stand on Zanzibar
by John Brunner (1969)

The genre's overpopulation classic is a near-future story of a crowded world where people are kept in check by brainy computers and mass-marketed psychedelics. Apparently mild-mannered Donald Hogan, a spy on a eugenics mission, is unaware that he has been programmed to kill. Eco-fear at its chilling best. A must for Brunner buffs.

The Gods Themselves
by Isaac Asimov (1972)

Rare Asimov stand-alone about energy transfers with a parallel universe. A small group learns the transference process used to acquire the seemingly abundant free energy will lead to the sun's annihilation. Peak of Asimov's maturation into a writer skilled in character development - the rebellious alien being particularly good.

The Sheep Look Up
by John Brunner (1972)

Classic cautionary tale about the dangers of unchecked pollution. The most cheerful thing Austin Train has in his life is the sight of flies. With all life dying out and living a life of poverty (despite having $600,000 in the bank), Train starts a radical terrorist movement to fight back. From there on, things really start to get grim. Certainly Brunner's most downbeat.

Timescape
by Gregory Benford (1980)

By 1998 uncontrollable pollution and social unrest has turned the world into a living hell. Two Cambridge scientists experiment with faster-than-light tachyons in an attempt to send a warning back in time to the early-1960s. Separate plotlines follow characters in both generations. Scientifically adept and extremely well-written.

Earth
by David Brin (1990)

A book that continues to grow in stature, Earth is a murder mystery of sorts set in the year 2038 - with good old Gaea herself the victim. While the issues of war and the effect of the information highway on modern society are examined, it the ecological messages that come through loud and clear. A real 'save the planet' excursion from one of sci-fi's best.

Green Mars [S2]
by Kim Stanley Robinson (1993)

Hugo-winning follow-up to the previous year's Red Mars. The philosophical split between the surviving scientists of the First Hundred colonists has one group appreciating Mars for what it is and the other advocating Earth-like terraforming. As the metanational corporations oversee the disintegration of Earth society, our heroes go on the lamb across the Martian landscape. Breathtaking.

Mother Of Storms
by John Barnes (1994)

Global warming is the villain in this tense techno-thriller that established Barnes' reputation as a topnotch sci-fi writer. When a pre-emptive missile strike releases vast quantities of methane into the atmosphere the resulting global warming unleashes massive killer hurricanes. A computer-charged astronaut tries to sort things out. Warms up well.