恐らく化石燃料を使い続ければ地球の気象は悪くなるでしょう。
I fear that if we continue to utilize fossil fuels that the Earth’s climate will probably worsen.
BTW, I wanted to add that I asked about the usage of ないで and 代わりに that was being discussed above over at HiNative and I was told by one Japanese person that in that situation they are both interchangeable. The meaning is the same as saying “Instead of X, I did Y”. IOW, Pablo’s translation was correct 
.
私の最初の文が短くなる。 文を書くのは意外に難しい！
My first sentence will be a short one. Writing sentences is surprisingly difficult!
初めは難しいけど、だんだん簡単になる。頑張ってね！
ちなみに、あなたは文の英訳を忘れた。書いてくれる? 
了解した
寝すぎなかったから、学ぶのは大変だった。 今夜、もっと寝るつもりだ。
サバンナは家をよく出かけて。
I am not sure how to say “from 家?”
Savannah often leaves home.
I believe you can use the case marking particle 「から」to mean “From”
サバンナは家から
The 「ている」Form of the verb can also be used to imply something is habitual, as in “Savannah often leaves home (As a habit).”
よく出かけています。
From these you get the finished sentence:
サバンナは家からよく出かけています。
If anyone else has anything to add feel free!
クッキーもうほとんど食べたけど、少しあるよ。
I’ve already eaten most of the cookies, but there’s still a few left.
クリスマス時に、この道で各家は美しくなります。
“At Christmas time, every house on this street becomes beautiful.”
Hi!
You would use the equivalent in Japanese to the present continuous: ～ている. Then, you would ‘ますfy’ the verb ‘いる’, thus: ～ています. In this particular case, this would result in 覚えています.
BTW, I didn’t know that 覚える could be used in this way, I thought it meant ‘to memorise’, ‘to remember’ or ‘to bear in mind’. I would have chosen 勉強する or maybe 学ぶ. Thank you!
一般相対性理論と量子力学は人類の最も効果的な理論です。
General Relativity and Quantum Mechanics are humanity’s most successful theories.
昨日は文がたくさんあっても、今日は一文もない。明日は文があるかどうか神のみぞ知るです。
Although there were a lot of sentences yesterday, today there is none. God only knows whether tomorrow there will be any.
I feel the same as you. Here’s a HiNative post related to this:
彼は一度失敗してからというもの、簡単に諦める嫌いがある。
“He has the tendency to easily quit after failing once.”
昨日映画館に行きました。スペイン語で「Perfect Days」をみましたが、日本語もわかりやすそうにみえるとおもいます。見なければ、勧めます。
Yesterday I went to the cinema. I saw Perfect Days in Spanish, but I think the Japanese would be easy to understand too. If you haven’t seen it, I recommend it.
人間は変えられるものだと信じていますが、彼は果敢になりそうもないと思います。
I believe that humans can change, but I don’t think he is likely to become bold.
昨日今日の天気予報を見て今日は晴れで暖かい日のはずだったからジャケットを着ずに働きに行くつもりだった。ところが、あまり暖かくなかったんだ。その結果、風邪を引いちゃった。 
Yesterday I looked at today’s weather forecast and, as it was bound to be a clear, warm day, I had the intention of going to work without wearing a jacket. However, it was not very warm. As a result of this, I cought a cold.
今日は休みをいいことにして、一日中友達とファイナルファンタジー14オンラインというゲームをしちゃった。
Taking advantage of my day off, I ended up spending all day playing a game called Final Fantasy 14 Online with a friend.
夜公園で数人が私を囲んで、「おい、兄さん、金をくれないか？」って、言い難い恐怖を感じた。
Several people surrounded me in the park at night, and I felt an indescribable fear as they said: ‘Hey, buddy, would you give us some money?’