The biggest environmental news of 1990 may turn out to have been its weather, the hottest ever recorded. But it will be several weeks before computers churn out the final measurements of 1990s global average temperature. Until then, notable events and trends of the past year size up like this.

Best: The United States' predicted solid waste crisis may be averted before it is fully upon us. Recycling is bursting out all over. From paper, plastics and magazines to Christmas trees, American consumers and corporations are tackling our mountains of garbage, most of which still goes to nearly full landfills.

In city after city, consumer participation in new recycling programs far exceeded predictions. Seattle recycled 37 percent of its waste in 1989, well on the way to its 60 percent goal in 1998. The city even makes "Seattle beige," a recycled latex paint. Recycling of newsprint was held back by a shortage of de-inking plants, but with the new capacity under construction in 1990, production will double by 1992. Exciting new technology developed this year for recycling magazines means that 30 percent to 40 percent of them could be recycled by mid-decade, up from less than 5 percent today.

Spurred on by consumer demand, some of the country's largest corporations are actually showing leadership. "We have identified a new consumer need not to feel guilty," said Procter and Gamble. While that hardly sounds inspiring, P&G Chairman E. L. Artzt told his shareholders this year that the United States can reduce its solid waste stream by an extraordinary 70 percent, and P&G will plan accordingly. The company, which already markets some of its products in 100 percent recycled plastic containers, plans to help develop large-scale municipal composting to replace landfills (in which almost nothing biodegrades), and said it would develop fully compostable disposable diapers.

Pepsi and Coca Cola simultaneously announced plans to market their sodas in recycled plastic bottles. McDonalds, under constructive pressure from the Environmental Defense Fund, abandonned its "clamshell" packages in favor of paper. By that single step the company reduced its volume of garbage by 90 percent and the national market for foam packaging (still made with atmospherically damaging chemicals) by 8 percent.

Oh yes, about Christmas trees. The Swedish retailer Ikea does a brisk business renting rather than selling trees. Upon return the trees are turned into mulch, which is given to the renter.

Fastest: The French TGV train continued to smash world speed records, beating 320 mph on May 18, confirming that the goal of commercial speeds of about 225 mph are achievable with conventional "steel wheels on steel rails" technology. At that speed, Boston and Washington are each one hour from downtown New York, and San Francisco less than 2 hours from Los Angeles. Europe plans a network of 19,000 miles of high speed rail lines by 2010.

Slowest: Congress completed a comprehensive rewrite of the Clean Air Act as the elapsed time clock neared 10 years. Former president Reagan gets most of blame, with House Commerce Committee Chairman John Dingell (D-Mich.) a solid second.

Missing: Almost half a year into its third oil crisis, the country seems not to notice that not having a national energy policy is costly. Among the questions yet to be addressed: What is the tolerable upper limit of U.S. dependence on oil imports? Fifty percent (about where we are today), 90 percent, lower? Is it wise to be the only industrialized country in the world that does not tax gasoline heavily? Have the others got it right, or do we? What are the economic consequences of an energy productivity level half as high as Japan's and Western Europe's? Are we willing to use price signals to improve energy efficiency, or should we rely solely on unpopular regulation?

Quote of the Year: We have a hands-down winner by J. R. Spradley, member of the U.S. delegation to a conference on climate change, addressing members of the delegation from Bangladesh. "This is not a disaster, it is merely a change. The area won't have disappeared, it will just be under water. Where you now have cows, you will have fish."

What to Watch for in 1991: The Bush administration plans to announce its version of a national energy strategy early in the year. Whether Congress can deal coherently with it is an open question. The endless energy battles of the 1970s have left lasting bruises on Capitol Hill. Members are loath to approach the subject again. The Democratic Party in particular lacks leadership -- policies and influential spokesmen for them -- on energy.

U.S. policy on greenhouse warming is a closely related question. In February the White House will host the first negotiations of an international global warming regime. Together with the Soviet Union, the United States is the only remaining industrialized holdout against targets to limit its carbon dioxide emissions. If U.S. policy doesn't shift, expect repercussions. The new world order is not only being shaped in the Persian Gulf.

New on the agenda next year will be how to come to grips with national over-reliance on the automobile. Environmental, energy, regional land preservation, urban neighborhood and other interest groups have finally realized that none of their various goals can be met without a more balanced approach to transportation. Look for an unprecedented attack on the Highway Trust Fund and related federal policies.

Jessica Mathews, a vice president of World Resources Institute, writes this column independently for The Post.