جمعه, مهر 29, 1390 03:28:00 ب.ظ

مدت­هاست که در بسیاری از منطقه­ های کره زمین از برف و سرمای همیشگی در زمستان و گرمای عادی تابستان­ها خبری نیست.

خشکسالی پیوسته افزایش می­یابد، آب آشامیدنی کمتر می­شود و انسان­ها با مشکل­های زیادی از قبیل سیل و طوفان و بیماری و کم شدن محصولات کشاورزی و ...بیشتر از قبل مواجه شده‌اند. علت تمام این اتفاق­ها، گرم شدن زمین و تغییرات آب و هوایی است، که نه تنها برای سلامتی و زندگی انسان‌ها خطرآفرین است بلکه حیات تمام موجودات روی زمین را تهدید می‌کند. اما «تغییر آب و هوایی» که این روزها در خبرها زیاد می‌شنویم چیست؟ شاید بسیاری از ما هنگامی که کلمه‌های «هوا» و «آب و هوا» را می‌شنویم، به طور دقیق ندانیم که تفاوت این دو در چیست. هوا در اطراف ما وجود دارد. شاید هوا اولین چیزی باشد که وقتی از خواب بیدار می‌شویم، به تغییر آن توجه می‌کنیم. اگر هوا سرد یا برفی باشد، برای بیرون رفتن لباس گرم به تن می‌کنیم و اگر هوا گرم و تابستانی باشد لباس خنک می‌پوشیم. چگونگی هوا می‌تواند در زمان بسیار کوتاهی تغییر کند؛ مثلاً ممکن است به مدت یک ساعت باران ببارد و سپس هوا صاف و آفتابی شود.

اما آب و هوا توصیفی از هوای جوی یک منطقه است که در مدت زمان طولانی‌تری، مثلاً یک سال بررسی می‌شود. اگر منطقه‌ای که هوای گرم و خشک دارد در مدت زمان مشخصی سردتر و یا بسیار گرم‌تر شود، دانشمندان می‌گویند که این منطقه دچار تغییرهای آب و هوایی شده است.

 

سیستم‌های آب و هوا چه هستند؟

اتمسفر­: اتمسفر که زمین را پوشانده، لایه نازکی است از ترکیب گازهایی که تنفس می‌کنیم. این لایه نازک مانند لباس به سرد و یا گرم شدن زمین کمک می­کند. سیستم‌های هوا که در اتمسفر پایین­تری گسترده شده­اند به واسطه گرمای تابیده شده از خورشید و گردش زمین و دگرگونی­های سطح زمین تغییرپذیر هستند.

اقیانوس­: 70 درصد سطح زمین را اقیانوس­ها پوشانده­اند. حجم زیاد آنها و خاصیت­هایی که دارند باعث شده مقدار زیادی گرما درون خود ذخیره کنند. اتمسفر و اقیانوس همیشه در حال تبادل ماده و انرژی هستند. به عنوان مثال، بخارهای آب از سطح اقیانوس وارد اتمسفر می‌شوند و این رطوبت به صورت باران و یا برف و حتی شبنم­های صبحگاهی به زمین باز می‌گردد.

خشکی­: 27 درصد سطح زمین را خشکی پوشانده است. خشکی‌ها انواع مختلف دارند. مثلاً وی‍ژگی‌های یک منطقه کوهستانی به طور کامل می‌تواند با یک منطقه هموار متفاوت باشد.

یخ: یخ بزرگ‌ترین منبع آب شیرین در کره زمین است که سه درصد سطح زمین را پوشانده است. یخ نقش مهمی در تنظیم کردن آب و هوا دارد.

بیوسفر : بیوسفر جایی است که موجودات زنده می‌توانند در آن زندگی کنند. گیاهان دی‌اکسیدکربن را می‌گیرند و اکسیژن به محیط وارد می‌کنند و حیوان‌ها برای تنفس اکسیژن را می‌گیرند و در بازدم دی اکسید کربن به هوا برمی‌گردانند و با این عمل مقدار زیادی دی اکسید کربن بین خشکی موجود در بیوسفر و فضای اتمسفر مبادله می‌شود.

تا به اینجا با معانی آب و هوا و جزءهای آن آشنا شدیم . حالا ببینیم که تغییرهای آب و هوایی به چه دلیل اتفاق می‌افتد و آیا تغییر شرایط دمایی کره زمین تأثیری بر آن دارد یا نه؟ ما می‌دانیم که کره زمین به طور طبیعی در اثر تابش نور خورشید گرم می‌شود. اما پدیده گرم شدن کره زمین مفهوم جدیدی است که با فعالیت‌های انسانی ارتباط مستقیم دارد و با تغییرهای طبیعی آن فرق می‌کند. مفهوم گرم شدن زمین، افزایش میانگین دمای کره زمین است که تغییرات آب و هوا در اثر این افزایش دما به وجود می‌آید. اگر دمای زمین فقط چند روز به بالای حد مجاز برسد، اهمیتی زیادی ندارد اما اگر این افزایش دما در مدت طولانی ادامه پیدا کند آن وقت نگران کننده می‌شود و در طولانی مدت مشکلات زیادی را برای طبیعت و انسان­ها به وجود می‌آورد. در طول صد سال گذشته کره زمین به طور غیر طبیعی 4/0 درجه سانتی‌گراد گرم‌تر از قبل شده است. همین میزان کم باعث به وجود آمدن مشکل‌های بزرگی شده است. به عنوان مثال گرم شدن بیش از حد می‌تواند بیماری‌هایی مثل گرما‌زدگی، ضعف و حالت تهوع را در پی داشته باشد. این اتفاق در نتیجه افزایش تعداد روزهای گرم سال رخ می‌دهد که در کشورهای فقیر و خشک مشکلاتی برای کودکان و افراد مسن ایجاد می‌کند. از طرف دیگر گرم شدن زمین باعث بالا رفتن سطح دریاها می­شود چرا که یخ‌های قطبی ذوب می‌شوند و آب بیشتری به اقیانوس‌ها اضافه می‌کنند. این اتفاق می تواند برای محیط زیست و انسان‌هایی که در نزدیکی اقیانوس زندگی می‌کنند خطرآفرین باشد.

شاید بپرسید گرم شدن زمین بر تغییرهای آب وهوایی چگونه تأثیر می‌گذارد، جواب این سؤال بسیار ساده است؛ با گرم شدن کره زمین شرایط آب وهوایی تغییر می‌کند. مثلاً آب و هوای برخی از مناطق کره زمین معتدل است و باران در آن منطقه‌ها به اندازه کافی می‌بارد و گرما و سرمای شدیدی ندارند. برعکس آب و هوای برخی از نقاط کره زمین سرد است و برف زیادی می‌بارد و همین طور مناطقی وجود دارند که دارای هوای گرم و خشک هستند. تغییرهای آب و هوایی باعث می‌شود در منطقه‌ای سرد از شدت سرما کاسته ‌شود و یا در منطقه‌ای خشک و گرم باران‌ زیاد ببارد و هوا سردتر از قبل شود.

نقل از: همشهری آنلاین

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