Honey, I Made the Earth Wobble! Not.

 

Image is from Honey, I Shrunk the Kids, a 1989 American science fiction family film produced by Walt Disney Pictures.

Repeated robotically by alarmist websites, this week’s climate scare says that burning fossil fuels is causing the earth to wobble in its spin.

Earth is Wobbling and Climate Change is to Blame Newsweek

Humans Are Causing Earth to Wobble Popular Mechanics

Human-Driven Climate Change Is Literally Making Earth ‘Wobble’ Motherboard

Earth’s rotation wobbles. NASA says humans partly to blame. Big Think

Earth’s Axis Is Drifting Inches Every Year In Part Because Of Human-Driven Climate Change IFLScience

Planet Earth Wobbles As It Spins, and Now Scientists Know Why Live Science  The case as made in the Live Science article,

Since 1899, the Earth’s axis of spin has shifted about 34 feet (10.5 meters). Now, research quantifies the reasons why and finds that a third is due to melting ice and rising sea levels, particularly in Greenland — placing the blame on the doorstep of anthropogenic climate change.

Another third of the wobble is due to land masses expanding upward as the glaciers retreat and lighten their load. The final portion is the fault of the slow churn of the mantle, the viscous middle layer of the planet.

Earth wobbles irregularly over time, which means it does not always spin on an axis running through its poles. Its axis has been drifting towards North America during most of the last century (green arrow). That direction has changed dramatically due to changes in water mass on Earth. (Image: NASA/JPS-Caltech)

After a little investigation, there are several reasons not to be alarmed about this finding.

1.The Wobble is ancient.

Scientists have long known that the distribution of mass around the Earth determines its spin, much like how the shape and weight distribution of a spinning top determines how it moves. Also, Earth’s spin isn’t perfectly even, as scientists know thanks to slight wiggles in the movements of the stars across the night sky that have been recorded for thousands of years, said Erik Ivins, a study co-author and a senior research scientist at JPL. Since the 1990s, space-based measurements have also confirmed that the Earth’s axis of rotation drifts by a few centimeters a year, generally toward Hudson Bay in northeastern Canada.

Researchers knew that a proportion of this wobble was caused by glacial isostatic adjustment, an ongoing process since the end of the last ice age 16,000 years ago. As the glaciers retreat, they relieve the land underneath of their mass. Gradually, over thousands of years, the land responds to this relief by rising like bread dough. (In some places on the edges of the ancient ice sheets, the land might also collapse because the ice had forced it to bulge upward.)

2. Wobbling results from multiple causes.

“We have provided evidence for more than one single process that is the key driver” for altering the Earth’s axis, said Surendra Adhikari, an Earth system scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, and a lead researcher on the new study.

But in the new research, published in the November issue of the journal Earth and Planetary Science Letters, Adhikari and his colleagues found that glacial isostatic adjustment was only responsible for about 1.3 inches (3.5 centimeters) of axis wobble per year. That was only about a third of the wobble — 4 inches (10.5 cm) — observed each year over the 20th century.

To fill in the gap, the research team built a computer model of the physics of Earth’s spin, feeding in data about changes in the balance of land-based ice and ocean waters over the 20th century. The researchers also accounted for other shifts in land and water, such as groundwater depletion and the building of artificial reservoirs, all part of humanity’s terraforming of the planet.

The results revealed that these environmental processes cause another 1.7 inches (4.3 cm) of wobble each year. The melting of the Greenland ice sheet was a particularly important contributor, the researchers found. That’s because Greenland has released a large amount of water that was once locked up on land into the oceans, where its mass has been redistributed, Ivins told Live Science. Mountain glaciers and small ice caps elsewhere have also contributed to sea-level rise, he said; but they aren’t as concentrated, and their effects on the Earth’s rotation often cancel each other out.

3. The mantle itself is always moving.

The glaciers and the ice melt still left a third of the wobble unaccounted for, so Adhikari and his team looked inward. The Earth’s mantle is not static, he said, but moves by the process of convection: Hotter material from closer to the core rises and cooler material sinks in a cycle of vertical motion. By including convection in the model of Earth’s wobble, the researchers had accounted for the last third of the changes in the spin over the 20th century.

4. The Wobble is not menacing.

It’s important to realize that this wobble isn’t the prelude to any sort of environmental calamity, Ivins and Adhikari said. It doesn’t affect agriculture or climate in and of itself, and any small impact on navigational equipment is easy to correct for.

“The amount [of drift] is not a huge amount,” Adhikari said.

5. Greenland ice sheet is affected by many natural factors.

A recent paper looked into unusually extensive melting in 2012. The implication of nonradiative energy fluxes dominating Greenland ice sheet exceptional ablation area surface melt in 2012 by Robert S. Fausto et al. Excerpts in italics with my bolds.

The surface energy budget consists of nonradiative (sensible, latent, rain, and subsurface) and radiative (shortwave and longwave) energy fluxes. Distinguishing the contribution of nonradiative and radiative energy fluxes in melt over the Greenland ice sheet is important to understand ice sheet surface climate sensitivity, especially in the ablation area, where the majority of melt occurs [e.g., Fausto et al., 2012a].

Ablation varies with elevation, but there are also considerable latitudinal differences as the Greenland ice sheet stretches from the upper midlatitudes (~60°N) to the high Arctic (~82°N). The largest total observed ice ablation in 2012 was 8.5 m ice eq. at QAS_L, which was 9% less than the 2010 value. This interannual variability may be attributed to larger winter snow accumulation in 2012, which maintained high surface albedo by delaying bare ice exposure during the melt season.

Given that absorbed solar radiation is the primary energy source of melt on an annual basis, the influence of intra‐annual and interannual variability in air temperature and other variables on ablation is of secondary importance [Van den Broeke et al., 2011]. Yet during the two melt episodes we focus on, which together resulted in ~14% of annual ice ablation (Table 1), the nonradiative (sensible, latent, rain, and subsurface) energy fluxes were the primary control of melt with a contribution of 53 ± 16% and 66 ± 8%, respectively, averaged for the eight western AWSs for episodes E1 and E2, respectively (Tables 1).

During the two episodes, the large longitudinal contrast in nonradiative energy fluxes contribution to surface melt stem from anomalously warm and moist southern air flow being transferred onto the western ice sheet by atmospheric flow (Figure 2b) [Neff et al., 2014; Bonne et al., 2015], while east Greenland was dominated by stable weather with relatively low cloud cover and high solar radiation (Figure 2c) [Fettweis et al., 2013; Tedesco et al., 2013].

More broadly, data from the two episodes presented here demonstrate that exceptional melt can occur during periods characterized by cloudy skies and transient atmospheric flow, with melt being dominated by nonradiative, rather than radiative fluxes in the ablation area.

Conclusions

We find that year 2012 Greenland ice sheet melt was marked not only by widespread interior surface melting [Nghiem et al., 2012] but also by an increased nonradiative (sensible, latent, and rain) energy flux contributing to melt in the ablation area of the southern and western ice sheet. Latent and sensible energy advection governed two exceptional melt episodes in July 2012 [Neff et al., 2014]. The two episodes which lasted just ~6% of the ablation period in June–August were responsible for ~14% of the annual 2012 ablation average for all PROMICE measurement sites (Table 1). At all PROMICE sites during the two exceptional melt episodes the combined sensible, latent, rain, and subsurface energy fluxes (i.e., nonradiative energy fluxes) comprised 60% of the melt energy on average (Figure 1 and Table S1).

Summary

Earth has wobbled a bit in its rotation since the beginning, and continues to do so. The movement is not large or menacing. The three causes appear to be shifting material in the mantle, land rebounding when glaciers retreat, and changes in Greenland ice sheet balance.

The latter is attributed to human activity, even though major melting events result primarily from nonradiative factors: sensible, latent, rain and subsurface energy fluxes. If you buy the notion that burning fossil fuels causes Greenland ice sheet to melt, then please contact me about my bridge in Brooklyn that I am selling.

One comment

  1. Hifast · September 26, 2018

    Reblogged this on Climate Collections.

    Like

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