Scientists simulate the effects of an asteroid collision

Last week, NASA announced that the asteroid 2024 YR4 has a greater than 2% chance of impacting Earth on 22 December 2032, increasing from the greater than 1% chance that was originally proposed on 29 January; the odds could continue to rise or fall as scientists gather more information about the asteroid.

But while there are global defence plans in place to cover such an event, it begs the question: how would climate and life on our planet change in response to a future asteroid strike? Researchers at South Korea’s IBS Center for Climate Physics (ICCP) set out to answer this question, with their results published in the journal Science Advances.

To determine the potential impacts of an asteroid strike on terrestrial and marine ecosystems, ICCP researchers simulated an idealised collision scenario with a medium-sized asteroid using a state-of-the-art climate model. They used as an example the asteroid Bennu, which has an estimated 1-in-2700 chance of colliding with Earth in September 2182 and a diameter of about 500 m. In contrast, the diameter of 2024 YR4 is estimated to be no more than 100 metres.

Using the supercomputer Aleph, the researchers ran several dust impact scenarios for a Bennu-type asteroid collision with Earth. In response to dust injections of 100–400 million tons into the upper atmosphere, the supercomputer model simulations show dramatic disruptions in climate, atmospheric chemistry, and global photosynthesis in the 3–4 years following the impact (Figure 1). For the most intense scenario, solar dimming due to dust would cause global surface cooling of up to 4°C, a reduction of global mean rainfall by 15%, and severe ozone depletion of about 32%. However, regionally, these impacts could be much more pronounced.

“The abrupt impact winter would provide unfavourable climate conditions for plants to grow, leading to an initial 20–30% reduction of photosynthesis in terrestrial and marine ecosystems. This would likely cause massive disruptions in global food security,” said Dr Lan Dai, postdoctoral research fellow at the ICCP and lead author of the study.

Figure 1: Climatic and ecological responses to dust injections of 400 million tons from a Bennu-type asteroid impact. Spatial changes of surface temperature (upper left), total precipitation (upper right), percentage change of terrestrial net primary productivity (lower left) averaged over the first 24 months, and percentage change of marine net primary productivity (lower right) averaged from 10 to 38 months after the impact relative to the control simulation. For a larger image, click here.

When the researchers looked into ocean model data from their simulations, they were surprised to find that plankton growth displayed a completely different behaviour. Instead of the rapid reduction and slow two-year-long recovery on land, plankton in the ocean recovered already within six months and even increased afterwards to levels not even seen under normal climate conditions.

“We were able to track this unexpected response to the iron concentration in the dust,” said Professor Axel Timmermann, Director of the ICCP and co-author of the study. Iron is a key nutrient for algae, but in some areas, such as the Southern Ocean and the eastern tropical Pacific, its natural abundance is very low.

Depending on the iron content of the asteroid and of the terrestrial material that is blasted into the stratosphere, the otherwise nutrient-depleted regions can become nutrient-enriched with bioavailable iron, which in turn triggers unprecedented algae blooms. According to the computer simulations, the post-collision increase of marine productivity would be most pronounced for silicate-rich algae — referred to as diatoms. Their blooms would also attract large amounts of zooplankton — small predators, which feed on the diatoms.

“The simulated excessive phytoplankton and zooplankton blooms might be a blessing for the biosphere and may help alleviate emerging food insecurity related to the longer-lasting reduction in terrestrial productivity,” Dai said.

Timmermann concluded, “On average, medium-sized asteroids collide with Earth about every 100–200,000 years. This means that our early human ancestors may have experienced some of these planet-shifting events before with potential impacts on human evolution and even our own genetic makeup.”

With the study providing insights into the climatic and biospheric responses to collisions with near-Earth objects, the ICCP researchers next plan to study early human responses to such events in more detail by using agent-based computer models, which simulate individual humans, their life cycles and their search for food.

Top image credit: iStock.com/solarseven