Friday, October 07, 2011

Celebrating the Advancement of Good Science: 2011 Nobel Prize in Physics has a Lesson for Climate Skeptics

By Gary Berg-Cross

Every fall I look forward to the awarding of the Nobel Prizes as a celebration of the core sciences, Literature, Peace and Economics, which seems to have elbowed its way into this group. This year Brian Schmidt, Saul Perlmutter & Adam Riess shared the 2011 Nobel prize in physics for their surprising 1998 discovery that the expansion of the universe is accelerating.

The fact that the observable universe was expanding and not static was an early 20th century discovery. A simple interpretation of observations seems was formulated mid-century that universe had been expanding since a fiery birth called the Big Bang some 13.7 billion years ago. If an explosion got it started it seemed logical that gravity would be slowing it down and the universe would collapse back together in what some called a Big Crunch.

That was the prevailing idea till Schmidt, Perlmutter & Riess looked back to early exploding stars (known as Type 1a supernovae) and measuring expansion over time. The results so an acceleration were so surprising that Riess spent weeks checking everything over and over to “make sure it wasn't a stupid error.” After a few weeks he couldn't find anything that seemed wrong and heard that 2 other teams — the Supernova Cosmology Project led by Perlmutter and the competing High-z Supernova Search team were puzzling over the same thing.

An interesting twist to the story is that in 1917, before the Big Bang theory a young Albert Einstein had adapted his of general theory relativity to explain such an acceleration. He suggested that there was a force, an intrinsic energy density that does not change with time that opposed gravity and kept the universe from collapsing into itself. He called it a cosmological constant but later dismissed this idea as a major blunder. But now decades later the idea seems to be a brilliant insight to explain some very exotic phenomena in the universe”

"It's a mysterious force... it may be three-quarters of all the stuff in the universe is this form and we did not know that before…..Really, we created a bigger question than we answered. ..We discovered that the universe is accelerating and it is filled with dark energy, but the question we created is, 'What is dark energy?' We don't understand the physics of it….It seems to live at the nexus between quantum mechanics and general relativity, two of our great theories of physics, but it lives just at that nexus where they don't work together.” said Riess, a professor of astronomy and physics at Johns Hopkins University in Baltimore, Maryland.

Something similar happened with climate change where scientists could see recent swings in climate and a series of ice ages. The natural world is full of cycles – seasons, sun activity and such. Three astronomical cycles the tilt of the earth, which varies over a 41,000 year period; the shape of the earth’s orbit, which changes over a period of 100,000 years; and the Precession of the Equinoxes, also known as the earth’s ‘wobble’ make up what is called as the Milankovitch cycles. Perhaps such things produce a regular pattern for the ebb and flow of ice sheets. By mid century a modest amount of data (from ice cores, ocean sediment cores, the geologic record, along with studies of ancient plant and animal populations) suggested that the recent warm, twelve thousand year-long Holocene period might soon be coming to an end. According to this we could be returning to Ice Age conditions and these might last for 100,000 years or so.This was popularized back in the 70s by an article or 2 on the coming ice age.

This is the type of old science which some climate change critics point back to as a counter to the idea that humans are changing the climate. It’s not that there aren’t other factors than humans that change the climate. It's just that they don't explain all the data including the new evidence. The rapid increase in greenhouse gases released by humans is a new factor whose effects we can increasingly test for. The more recent and detailed evidence provides a distrubing view of the forcing effect of greenhouse gases on climate.

This slow advancement and deepening of scientific explanation mixed with new mysteries it turns up is one thing that many climate change critiques fail to acknowledge. We learn part of the big picture – the universe is expanding – but don’t have all the details at one moment. Conflicting hypotheses may exist and require new data to settle. In the case of climate change it’s not as if the climate science avoids these cycles. Indeed modern modeling can address such issues in sophisticated ways. For example, the IPCC report includes Frequently Asked Question and 6.1 of these asks - “What Caused the Ice Ages and Other Important Climate Changes Before the Industrial Era?”

Part of the answer is that a small initial cooling due to the Milankovitch cycles is subsequently amplified as the CO2 concentration falls. As they note:

“Model sim­ulations of ice age climate (discussed in Section 6.4.1 of the IPCC report) yield realistic results only if the role of CO2 is accounted for.

During the last ice age, over 20 abrupt and dramatic climate shifts occurred that are particularly prominent in records around the northern Atlantic …. These differ from the gla­cial-interglacial cycles in that they probably do not involve large changes in global mean temperature: changes are not synchro­nous in Greenland and Antarctica, and they are in the opposite direction in the South and North Atlantic. This means that a major change in global radiation balance would not have been needed to cause these shifts; a redistribution of heat within the climate system would have sufficed. There is indeed strong evidence that changes in ocean circulation and heat transport can explain many features of these abrupt events; sediment data and model simula­tions show that some of these changes could have been triggered by instabilities in the ice sheets surrounding the Atlantic at the time, and the associated freshwater release into the ocean.”

It’s nice to celebrate good science.

No comments: