(NEW YORK) — As Russia’s military gears up for what it hopes will be a decisive victory over Ukraine in the eastern part of the country, the U.S. is rushing to send weapons and equipment needed to hold off the larger invading force in the rural and open Donbas terrain — a far different battlefield from the urban fighting where Ukrainian forces held an advantage.

What could make all the difference now is the new $800 million military aid package for Ukraine President Joe Biden announced Thursday.

It’s a race against time — maybe a matter of weeks, a U.S. defense official said.

“Now they’ve launched and refocused their campaign to seize new territory in eastern Ukraine, and we’re in a critical window now of time where they’re going to set the stage for the next phase of this war,” Biden said of the Russian offensive, which U.S. military officials believe is just getting started.

“We know that time is not our friend,” Pentagon press secretary John Kirby told reporters Tuesday.

Russia gains by being closer to its border

With Ukrainian forces focused in the east, Russia intends to push down from the north, near the city of Izium, and up from the south, surrounding the Ukrainian defenders to “finish them or force them to surrender,” a senior U.S. official said Thursday.

If Russia takes the beleaguered city of Mariupol in the south, it could free up thousands of troops to join the push north to trap Ukraine forces, according to the official.

Although Russia and Ukraine have been battling over Donbas for eight years, Russia’s concentrated flow of troops and weapons into the region could bring “a whole different level of fighting,” Kirby said Tuesday.

There are now 85 battalion tactical groups (BTGs), Russia’s main fighting units, inside Ukraine, according to the official. Each BTG is made up of roughly 800-1,000 troops. About 10 of them crossed into the country this week, most heading to the Donbas region.

Kirby said the U.S. is focused on sending Ukraine weapons and systems that are not only useful for the rural eastern terrain, but that the Ukrainians can use in the fight without much training.

Russia, meanwhile, is trying not to repeat blunders it committed in northern Ukraine, and will enjoy certain geographic advantages in Donbas.

Early on, Russian invaders in the north were beset by supply problems, running out of food for troops and fuel for vehicles, failing to achieve any major victories. Pentagon officials believe they did not expect such strong resistance from Ukrainians so they didn’t adequately prepare for a prolonged fight.

But since withdrawing its troops in the north to focus on Donbas, Russia has been putting equipment and support forces in place ahead of its combat troops to favorably condition the battlefield.

“We believe that they are trying to learn from past mistakes, and you can see that in just the way they are conducting these shaping operations,” Kirby told reporters Monday. “They’re conducting themselves in ways that we didn’t see around Kyiv, for instance.”

Another advantage for Russia is that its logistics will be simplified by fighting closer to its own border, while Ukraine will now face the challenge of transporting heavy weapons and ammunition coming over its western border all the way across the country, meaning more miles for something to go wrong, and more chances for Russia to strike these vital shipments.

How US-provided artillery and radars could make a difference

To stand a chance fighting in the open Donbas landscape, Ukraine will need more long-range weapons and the ability to quickly move troops on the ground and in the air, according to Mick Mulroy, former deputy assistant secretary of defense for the Middle East and ABC News contributor.

The U.S. has sent Ukraine $3.4 billion of aid since the beginning of the invasion, including many thousands of shoulder-fired missiles, small arms and ammunition, body armor, and medical supplies. The two most recent packages, dedicating $800 million of aid each, announced April 13 and 21, were tailored to reflect the new battle space.

“It’s different,” Biden said Thursday. “It’s flat, it’s not in the mountains, and it requires different kinds of weapons to be more effective.”

To that end, the U.S. is sending 90 of its 155mm howitzers, which officials say will begin arriving over the weekend.

“This is going to be the king of battle out there,” Mulroy said.

While Ukraine already has Russian-made artillery pieces, the U.S. and most Western nations do not have the corresponding 152mm ammunition to offer as it runs through its limited stockpiles. The incoming U.S.-made 155mm guns will bring Ukrainian forces extra firepower, but also the ability to be better resupplied by the West.

To start, the U.S. is sending 184,000 artillery rounds along with the 90 weapons.

Russia has been flowing its own artillery into Donbas in preparation for its renewed offensive. To help Ukraine counter the threat, the U.S. is sending 14 radar systems that can detect incoming artillery and other indirect-fire attacks and find where they’re coming from.

“Right now the Russians are kind of just lobbing artillery without any consequence,” Mulroy said. “They want to give them a whole lot of consequence.”

The radar systems can help the Ukrainians accurately fire back.

“The counter radar is moving to theater this week,” a senior U.S. defense official said Thursday, adding that the howitzers and radar systems complement each other, but can also be used independently.

Training will be critical

About 50 Ukrainians are being trained on the U.S. howitzers outside of the country. This first group of trainees is expected to finish around the same time as the first artillery pieces arrive in their country, likely Sunday or Monday, according to a U.S. official. The U.S. is using a “train-the-trainer” approach so as not to pull too many high-demand troops away from the front — the small group of Ukrainians learning to use the new systems will return to their country to train fellow Ukrainian troops there.

The U.S. took a similar approach with the small, explosive Switchblade drones, hundreds of which are headed to Ukraine.

A small number of Ukrainians were in the U.S. for pre-scheduled military education when Russia invaded their country. The U.S. capitalized on their presence to add a couple days of training on the Switchblades, which are designed to fly directly into targets and explode.

“Although it’s not a very difficult system to operate, we took advantage of having them in the country to give them some rudimentary training on that,” a U.S. defense official said on April 6.

U.S. officials have said other systems being sent to Ukraine will also require a small period of training, likely to also take place outside of the country. Officials have declined to specify where such training could take place, citing operational security concerns.

With Russia intent on surrounding and trapping Ukrainian forces, the ability to move troops quickly by ground and air will be essential, according to Mulroy.

“They’re going to try to envelope the Ukrainians and cut them off and starve them,” he said. “So, the Ukrainians need to have the ability not to let that happen.”

Since the beginning of the invasion, the U.S. has given Ukraine 16 Mi-17 transport helicopters, each able to carry a three-person crew and up to 30 passengers.

Mulroy said an advantage of the Soviet-designed Mi-17 is that Ukrainian pilots already know how to fly them.

The U.S. has also offered Ukraine hundreds of armored personnel carriers that have tracks similar to those of tanks, as well as armored Humvees.

Weather will likely play a factor, and muddy conditions during Spring could limit vehicle mobility for both sides.

“Even just this week, the ground as it is makes it harder for them to operate off of paved roads and highways,” Kirby said.

Time is of the essence

Mulroy said the U.S. is doing a great job shipping military aid to the region, but believes more can be done to speed things up.

“We just have to take every opportunity to increase production and improve the flow, because it is going to make a difference,” he said.

The U.S. has not sent Ukraine any of its M1 Abrams tanks, officials saying they are too different from Ukraine’s T-72s to be useable in the short term. But other nations with the Soviet-era tanks have given theirs.

In total, Ukrainian forces have more tanks in their country than Russia’s military, a senior U.S. defense official said Thursday.

A less tangible but very real factor in the fighting so far has been troop morale.

The Pentagon sees evidence Russian forces are still suffering from low motivation and poor unit cohesion, according to officials.

“Almost half of their enlisted troops are conscripts who don’t receive a lot of training and who we have evidence, even recent evidence, that they’ve been disillusioned by this war,” the senior U.S. defense official said.

Meanwhile Russian officers are frustrated with the performance of other officers and of their own troops, according to the official.

Ukrainian troops have not seemed to suffer any significant morale problems, and throughout the war have been described by U.S. officials as brave and wily in defense of their homeland.

Biden praised the resolve of Ukrainians in a meeting with top military leaders at the White House Wednesday.

“I knew they were tough and proud, but I tell you what, they’re tougher and more proud than I thought,” Biden said.

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(NEW YORK) — The ability for polar bears to survive in coming decades is becoming more uncertain as global warming continues to melt the Arctic at unprecedented rates, experts warn.

Now, biologists and conservationists determined to save the species have zeroed in on a plan to increase populations: focus on the survival of mothers and cubs, who find themselves increasingly vulnerable to dwindling habitat and food sources, they tell ABC News.

The “fundamental” key to the survival of polar bears is the availability of sea ice cover, Louise Archer, a researcher at the University of Toronto Scarborough’s Department of Biological Sciences, told ABC News.

The Arctic is currently warming twice as fast as the rest of the planet, according to the Arctic Report Card published by the National Oceanic and Atmospheric Administration in December, leaving the Arctic in a “dramatically different state,” with a substantial decline since 1979.

It takes an incredible amount of energy for mothers to raise their cubs, but ironically they are not the most efficient hunters, Archer said. They rely on the sea ice as a platform from which to access marine mammals from.

“So having access to sea ice is extremely important to ensure the survival of adults, but also, so that females can support the survival of their cubs,” Archer said.

One of the “biggest challenges” from global warming is bears will have to respond to sea ice conditions, or the lack thereof, that have never been experienced in the Arctic before, she said.

Polar bear mothers, especially, need nutrients because they lactate for up to two-and-a-half years, the entire time “the cubs are taking in energy from their moms,” Archer said.

When the cubs are born in the den, they only weigh about a pound or two, she said. But their mother has to raise them to about 10 to 20 pounds before she can go out onto the sea ice and hunt again.

All the months in hibernation are not spent sleeping. The mother is nursing, grooming the cubs and maintaining the den, which involves scratching the ceiling and walls with her claws to allow airflow. Otherwise, the den would get completely iced over, and no oxygen would be able to get in, Geoff York, senior director of conservation group Polar Bears International, told ABC News.

The mothers and cubs begin to emerge from their dens after four to eight months of not eating or drinking. The priority is to build up fat stores before the sea ice begins to melt in the summer. But if the sea ice is melting sooner, that’s less time for the mothers to hunt — and to teach her children to do so — and less time to regain the fat stores they lost while fasting and lactating in the den.

“Anything that sort of interrupts that sequence is potentially fatal to the reproductive attempt of the female,” Andrew Derocher, a professor of biological science at the University of Alberta, told ABC News. “It’s a chain of events that is incredibly sensitive to things like sea ice break up in the springtime — and that’s one of the key metrics that we monitor, is when is the ice breaking out.”

Derocher believes the mother-cub relationship is so integral because it is an “incredible part of their life history.” After they leave the den, the mothers have an incredible task of teaching the cubs to swim, hunt and one day survive on their own.

It is that relationship that provides a “powerful emotion and a very forceful narrative” for Disney’s new film Polar Bear, which follows a mother with her cubs as they embark on that journey, Alastair Fothergill, one of the directors of the film, told ABC News.

In the first years of a polar bear’s life, they are “extraordinarily dependent on their mother,” said Fothergill, who has been filming in the Arctic for more than 25 years.

The biggest change Fothergill has witnessed as a result of the ice melting is the new tricks mothers are teaching their cubs, such as climbing cliffs to get bird eggs and chicks, as well as learning to hunt walrus calves — a dangerous feat, as the mother walruses defend their young with their tusks. Previously, seals served as their primary source of food.

Experts have found that the health of a polar bear population can be determined by “three good winters,” York said. Last year, he witnessed a mother with triplet cubs in the Western Hudson Bay of Canada — an increasingly rare sight in a population that has declined 30% in the last 40 years.

“That’s kind of what polar bears need,” he said. “They need three good years to bring cubs from birth to sub adulthood and get them out of the sub population.”

One of the most profound phases of the mother-cub relationship is the moment the mother must leave her cubs, a “really risky and dangerous time for the polar bear,” he said.

“We say in the narrative that she knew she had taught her cubs everything she could, which is true,” he said. “But at the same time, she has to move on. She has to go and have another set of cubs.”

Researchers have found that in more solitary populations of polar bears that have had less access to sea ice, the bears are forced to fast for longer periods of time, Archer said. This has led to a decline of body condition, the decline in the survival of colds and the decline in the overall population abundance, she added.

The bears who live in the most southern regions are more at risk, and there could very well be a time when the subpopulations in the Arctic are the only ones to persist, Archer said. Places like Wrangel Island off of Russia offer a place for polar bears to retreat during times of significant ice loss, where they have access to walrus, York said.

Given the current climate change conditions, the ability for polar bears to feed and survive will become increasingly precarious — unless they can adapt and learn how to survive on terrestrial land, Archer hypothesized.

“Once the ice is inaccessible to bears, survival of bears is severely compromised,” she said.

When Derocher published a paper in 1993 about the potential effects of warming on polar bears, he did not think he would see those effects within his lifetime, he said.

“We thought this is something for future generations far away,” he said. “And what has surprised me is that the changes have been manifest in the populations so much sooner than we anticipated.”

It will be human activity and the ability for it to properly mitigate climate change that will ultimately determine the chances for polar bears to survive, York said. They are currently listed as vulnerable on the International Union for Conservation of Nature’s Red List of Threatened Species.

“That’s directly tied to actions we may or may not take to curb our greenhouse gas reductions,” he said.

You can stream Disney’s Polar Bear”starting on April 22 on Disney+. The Walt Disney Company is the parent company of ABC News.

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