Birders once upon a time reasonably hoped that spring would arrive a bit late, trees not fully greened before migrant birds arrived. Fewer, smaller leaves, better birding.

That most likely is a thing of the past. It certainly isn't going to happen this year. The maple trees in our yard are in full bloom, leaves soon to follow blossoms.

Paul Douglas, weather columnist and blogger for the StarTribune, tells us that so far this is the second warmest Minnesota March on record. Ice went out on Lake Minnetonka on the second earliest known date ever, and left Cedar and White Bear lakes the earliest recorded date ever.

Weather records kept at Manoa Observatory in Hawaii show that February was the warmest since 1880. Carbon dioxide content of the air (CO2 drives temps up) averaged 404.16 parts per million (ppm) in February, up from an average of 400.13 in 2015. Daily CO2 measurement for Sunday, March 20, was 405.21 ppm.

The highest-ever daily average CO2 reading of 407.12 ppm occurred on March 18. That's very high.

Reaching and passing 400 ppm is regarded as a disheartening milestone in these ongoing measurements. Scientists doubt if we will slip below 400 ppm again. That means that whatever impact that CO2 is having on our weather today will never lessen. It can be held steady, which you see is not happening, or it can grow.

These measurements are made by two independent CO2 monitoring programs, the National Oceanic and Atmospheric Administration and the Scripps Institution of Oceanography. Data is posted to www.co2.earth.

Good news about spring in our yard is return of our pair of nesting Canada geese, a pair of Hooded Mergansers that used one of our duck boxes for nesting last year, and six pairs of Wood Ducks. The Sandhill Cranes that have nested just west of us for several years also are back on territory.

The metro area is full of waterfowl. There are ducks on a pond near you.